Add Style configuration

The following functionalities are added to configure aerc ui styles.
- Read stylesets from file with very basic fnmatch wildcard matching
- Add default styleset
- Support different stylesets as part of UiConfig allowing contextual
  styles.
- Move widgets/ui elements to use the stylesets.
- Add configuration manual for the styleset

2 files changed, 203 insertions, 0 deletions

diff --git a/doc/aerc-config.5.scd b/doc/aerc-config.5.scd
index eb88849..3ff5177 100644
--- a/doc/aerc-config.5.scd
+++ b/doc/aerc-config.5.scd
@@ -173,6 +173,20 @@ These options are configured in the *[ui]* section of aerc.conf.
 
 	Default: 250ms
 
+*stylesets-dirs*
+	The directories where the stylesets are stored. The config takes a
+	colon-seperated list of dirs.
+
+	Default: "/usr/share/aerc/stylesets"
+
+*styleset-name*
+	The name of the styleset to be used to style the ui elements. The
+	stylesets are stored in the 'stylesets' directory in the config
+	directory.
+
+	Default: default
+
+
 ## Contextual UI Configuration
 
 The UI configuration can be specialized for accounts, specific mail
diff --git a/doc/aerc-stylesets.7.scd b/doc/aerc-stylesets.7.scd
new file mode 100644
index 0000000..5b4cd37
--- /dev/null
+++ b/doc/aerc-stylesets.7.scd
@@ -0,0 +1,189 @@
+aerc-stylesets(7)
+
+# Name
+
+aerc-stylesets - styleset file specification for *aerc*(1)
+
+# SYNOPSIS
+
+aerc uses a simple configuration syntax to configure the styleset for
+its ui.
+
+# Styleset Configuration
+
+Aerc uses a simple configuration file to describe a styleset. The
+styleset is described as key, value pairs. In each line, the key
+represents the style object it signifies and the color/atrribute of
+that is modified.
+
+For example, in the line below, the foreground color of the
+style object "msglist_unread" is set to "cornflowerblue"
+```
+msglist_unread.fg=cornflowerblue
+```
+
+The configuration also allows wildcard matching of the style_objects
+to configure multiple style objects at a time.
+
+## Style
+The following options are available to be modified for each of the
+style objects.
+
+*fg*
+	The foreground color of the style object is set.
+
+	Syntax: `<style_object>.fg=<color>`
+
+*bg*
+	The background color of the style object is set.
+
+	Syntax: `<style_object>.bg=<color>`
+
+*bold*
+	The bold attribute of the style object is set/unset.
+
+	Syntax: `<style_object>.bold=<true|false|toggle>`
+
+*blink*
+	The blink attribute of the style object is set/unset.
+	_The terminal needs to support blinking text_
+
+	Syntax: `<style_object>.bold=<true|false|toggle>`
+
+*underline*
+	The underline attribute of the style object is set/unset.
+	_The terminal needs to support underline text_
+
+	Syntax: `<style_object>.underline=<true|false|toggle>`
+
+*reverse*
+	Reverses the color of the style object. Exchanges the foreground
+	and background colors.
+
+	Syntax: `<style_object>.reverse=<true|false|toggle>`
+	_If the value is false, it doesn't change anything_
+
+*normal*
+	All the attributes of the style object are unset.
+
+	Syntax: `<style_object>.normal=<true>`
+	_The value doesn't matter_
+
+*default*
+	Set the style object to the default style of the context. Usually
+	based on the terminal.
+
+	Syntax: `<style_object>.default=<true>`
+	_The value doesn't matter_
+
+## Style Objects
+The style objects represent the various ui elements or ui instances for
+styling.
+
+[[ *Style Object*
+:[ *Description*
+|  default
+:  The default style object used for normal ui elements while not
+   using specialized configuration.
+|  error
+:  The style used to show errors.
+|  warning 
+:  The style used when showing warnings.
+|  success
+:  The style used for success messages.
+|  title
+:  The style object used to style titles in ui elements.
+|  header
+:  The style object used to style headers in ui elements.
+|  statusline_default
+:  The default style applied to the statusline.
+|  statusline_error
+:  The style used for error messages in statusline.
+|  statusline_success
+:  The style used for success messages in statusline.
+|  msglist_default
+:  The default style for messages in a message list.
+|  msglist_unread
+:  Unread messages in a message list.
+|  msglist_read
+:  Read messages in a message list.
+|  msglist_deleted
+:  The messages marked as deleted.
+|  msglist_marked
+:  The messages with the marked flag.
+|  msglist_flagged
+:  The messages with the flagged flag.
+|  dirlist_default
+:  The default style for directories in the directory list.
+|  completion_default
+:  The default style for the completion engine.
+|  completion_gutter
+:  The completion gutter.
+|  completion_pill
+:  The completion pill.
+|  tab
+:  The style for the tab bar.
+|  stack
+:  The style for ui stack element.
+|  spinner
+:  The style for the loading spinner.
+|  border
+:  The style used to draw borders. *Only the background color is used*.
+|  selecter_default
+:  The default style for the selecter ui element.
+|  selecter_focused
+:  The focused item in a selecter ui element.
+|  selecter_chooser
+:  The item chooser in a selecter ui element.
+
+## fnmatch style wildcard matching
+The styleset configuration can be made simpler by using the fnmatch
+style wildcard matching for the style object.
+
+The special characters used in the fnmatch wildcards are:
+[[ *Pattern*
+:[ *Meaning*
+|  \*
+:  Matches everything
+|  \?
+:  Matches any single character
+
+For example, the following wildcards can be made using this syntax.
+[[ *Example*
+:[ Description
+|  \*.fg=blue
+:  Set the foreground color of all style objects to blue.
+|  \*list.bg=hotpink
+:  Set the background color of all style objects that end in list 
+   to hotpink.
+
+## Selected modifier
+Selected modifier can be applied to any style object. The style provided for
+the selected modifier are applied on top of the style object it correspons to.
+
+If you would like to make sure message that are flagged as read in the msglist
+appear in yellow foreground and black background. You can specify that with
+this.
+
+\tmsglist_default.selected.fg=yellow
+\tmsglist_default.selected.bg=black
+
+If we specify the global style selected modifer using fnmatch as below:
+
+\t\*.selected.reverse=toggle
+
+This toggles the reverse switch for selected version of all the style objects.
+
+## Colors
+The color values are set using the values accepted by the tcell library.
+The values can be one of the following.
+
+	*default*
+		The color is set as per the system or terminal default.
+
+	*<Color name>*
+		Any w3c approved color name is used to set colors for the style.
+
+	*<Hex code>*
+		Hexcode for a color can be used. The format must be "\#XXXXXX"
+