Adds support for the ``.. code::`` rst directive.

This modifies the existing ``.. code-block::`` to be treated as spec
extension with a specific default language syntax. Also implements line
numbering.
Modifies docgen to support new warning message.
Improves macro tutorial with hyperlinks and numbered lines.
Hyperlinks quit related docstrings in system module.
Hyperlinks slurp related docstrings in system module.
Handles :file: option for code blocks to avoid warnings.
the big renamefest: first steps
system files use new identifiers
renamefest
renamefest
big rename
big rename
big rename
big rename
big rename
updated base64.nim
updated basic2d, basic3d modules
more modules updated
more modules updated
more modules updated