Fix many broken links and prefer relative links within docs (#12463)

* Fix many broken links

Note that contrary to what docgen.rst currently says, the ids have
to match exactly or else most web browsers will not jump to the
intended symbol.

* Prefer relative links for Nim documentation

This is more friendly to those browsing the documentation without
a network connection. The nim-doc package in Debian allows this,
for example.

Also, the domain name being used was not consistent. It could have
been either nim-lang.org or nim-lang.github.io, and those reading
the stable docs could have found themselves suddenly reading the
devel docs instead.

* koch.rst: remove link to nonexistent section

* manual.rst: remove unintended link

cast[T](0) is interpreted as a link to id 0 with text T, so escape
the opening parentheses to display the intended output.

* asyncstreams: replace unintended link with emphasis

* Fix word wrapping

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/std/sha1.nim b/lib/std/sha1.nim
index 0099d5f6d..8f35a44ff 100644
--- a/lib/std/sha1.nim
+++ b/lib/std/sha1.nim
@@ -211,7 +211,7 @@ proc secureHashFile*(filename: string): SecureHash =
   ## Generates a ``SecureHash`` from a file.
   ##
   ## **See also:**
-  ## * `secureHash proc <#secureHash,string>`_ for generating a ``SecureHash`` from a string
+  ## * `secureHash proc <#secureHash,openArray[char]>`_ for generating a ``SecureHash`` from a string
   ## * `parseSecureHash proc <#parseSecureHash,string>`_ for converting a string ``hash`` to ``SecureHash``
   secureHash(readFile(filename))
 
@@ -219,7 +219,7 @@ proc `$`*(self: SecureHash): string =
   ## Returns the string representation of a ``SecureHash``.
   ##
   ## **See also:**
-  ## * `secureHash proc <#secureHash,string>`_ for generating a ``SecureHash`` from a string
+  ## * `secureHash proc <#secureHash,openArray[char]>`_ for generating a ``SecureHash`` from a string
   runnableExamples:
     let hash = secureHash("Hello World")
     assert $hash == "0A4D55A8D778E5022FAB701977C5D840BBC486D0"
@@ -231,7 +231,7 @@ proc parseSecureHash*(hash: string): SecureHash =
   ## Converts a string ``hash`` to ``SecureHash``.
   ##
   ## **See also:**
-  ## * `secureHash proc <#secureHash,string>`_ for generating a ``SecureHash`` from a string
+  ## * `secureHash proc <#secureHash,openArray[char]>`_ for generating a ``SecureHash`` from a string
   ## * `secureHashFile proc <#secureHashFile,string>`_ for generating a ``SecureHash`` from a file
   runnableExamples:
     let