Python API documentation generation tool Code

- Removed unnecessary <code class="pyval">...</pyval> wrapping element
from the output of the PyvalColorizer.

- Modified pyval_repr.py so now it generates a ParsedEpydocDocstring
as its output. This should make it possible to change
APIDoc.pyval_repr to return a ParsedDocstring instead of a str.
This ParsedDocstring would be the result of colorization via
pyval_repr, with the parsed repr as a fallback.

- Added preliminary repr tests

- Refactored some test functions

- Added a new module for colorizing python values. This abstracts away
from the code that's currently in the html writer, and should make it
easier to use the same colorization code for other docwriters. The
new code should do a better job of pretty-printing values than the
current html writer code. I also fixed a couple minor bugs in the
regexp colorizer along the way.

Note, though, that this code hasn't been plugged into epydoc in any
way yet. I.e., docwriter/html.py still needs to be modified to actually
*use* this new code.

- Added options to control return value::

--fail-on-error
--fail-on-warning
--fail-on-docstring-warning

All three options cause epydoc to exit with status 1 if a message of
the indicated level or higher is generated. This can be useful for
e.g., incorperation into makefiles. (See sf bug 1558792)

- Added --simple-term option, which tells epydoc not to use any color
or cursor control, even if the terminal appears to support it.

- Fixed SF bug 1562530, which causes nested literal braces to not
get parsed correctly.

- Explicitly specify that the stylesheet should be linked (not
embedded).

- Replaced implementation of doctest-html target with a more makefile-like
one (the old one use a shell script; and in the comments for SF bug
#1655963, someone indicated that it wasn't working for them.)