Python API documentation generation tool Code

- 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.)

- Fixed minor markup error

- Moved various test functions from doctest files (eg, runbuilder,
runparser, etc) to a single epydoc.test.util module, so they can
be shared between different doctest files. (E.g., the
restructuredtext.doctest file needed to make use of the
runbuilder function defined in docbuilder.doctest).
- Moved all tests that depend on docutils to restructuredtext.doctest
- Marked restructuredtext.doctest as requiring the docutils module

- Added support for adding ':RequireModule:' fields to doctest test
files, which assert that the tests shouldn't be run unless that
module is available. Used by restructuredtext.doctest to prevent
the tests from being run if the docutils module is not installed.

- Moved various test functions from doctest files (eg, runbuilder,
runparser, etc) to a single epydoc.test.util module, so they can
be shared between different doctest files. (E.g., the
restructuredtext.doctest file needed to make use of the
runbuilder function defined in docbuilder.doctest).