* Implement Markdown indented code blocks
Additional indentation of 4 spaces makes a block an "indented code block"
(monospaced text without syntax highlighting).
Also `::` RST syntax for code blocks is disabled.
So instead of
```rst
see::
Some code
```
the code block should be written as
```markdown
see:
Some code
```
* Migrate RST literal blocks :: to Markdown's ones
- 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
