Improve Markdown code blocks & start moving docs to Markdown style (#19954)

- add additional parameters parsing (other implementations will just
  ignore them). E.g. if in RST we have:

  .. code:: nim
     :test: "nim c $1"

     ...

  then in Markdown that will be:

  ```nim test="nim c $1"
  ...
  ```

- implement Markdown interpretation of additional indentation which is
  less than 4 spaces (>=4 spaces is a code block but it's not
implemented yet). RST interpretes it as quoted block, for Markdown it's
just normal paragraphs.
- add separate `md2html` and `md2tex` commands. This is to separate
  Markdown behavior in cases when it diverges w.r.t. RST significantly —
most conspicously like in the case of additional indentation above, and
also currently the contradicting inline rule of Markdown is also turned
on only in `md2html` and `md2tex`. **Rationale:** mixing Markdown and
RST arbitrarily is a way to nowhere, we need to provide a way to fix the
particular behavior. Note that still all commands have **both** Markdown
and RST features **enabled**. In this PR `*.nim` files can be processed
only in Markdown mode, while `md2html` is for `*.md` files and
`rst2html` for `*.rst` files.
- rename `*.rst` files to `.*md` as our current default behavior is
  already Markdown-ish
- convert code blocks in `docgen.rst` to Markdown style as an example.
  Other code blocks will be converted in the follow-up PRs
- fix indentation inside Markdown code blocks — additional indentation
  is preserved there
- allow more than 3 backticks open/close blocks (tildas \~ are still not
  allowed to avoid conflict with RST adornment headings) see also
https://github.com/nim-lang/RFCs/issues/355
- better error messages
- (other) fix a bug that admonitions cannot be used in sandbox mode; fix
  annoying warning on line 2711

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/nim.nim b/compiler/nim.nim
index bfb07ba20..48472507d 100644
--- a/compiler/nim.nim
+++ b/compiler/nim.nim
@@ -122,7 +122,7 @@ proc handleCmdLine(cache: IdentCache; conf: ConfigRef) =
         # `The parameter is incorrect`
       let cmd = cmdPrefix & output.quoteShell & ' ' & conf.arguments
       execExternalProgram(conf, cmd.strip(leading=false,trailing=true))
-    of cmdDocLike, cmdRst2html, cmdRst2tex: # bugfix(cmdRst2tex was missing)
+    of cmdDocLike, cmdRst2html, cmdRst2tex, cmdMd2html, cmdMd2tex: # bugfix(cmdRst2tex was missing)
       if conf.arguments.len > 0:
         # reserved for future use
         rawMessage(conf, errGenerated, "'$1 cannot handle arguments" % [$conf.cmd])