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.
Add list comprehensions to future module
Extend list comprehension documentation
Add -lm for fesetround and fegetround
Move floating point rounding and exceptions handling to math
(it's C99 as well, not just POSIX)
Move fenv to its own module
the big renamefest: first steps
system files use new identifiers
renamefest
renamefest
big rename
big rename
big rename
big rename
big rename