Python API documentation generation tool Code

- Check that duplicate item names are not given to build_doc_index;
if they are, then issue a warning and discard dups.
- Check that we don't generate 2 doc items with the same canonical name
from different items. This can happen, e.g., if you run
"epydoc a/x.py b/x.py" where neither a nor b are package directories,
so both modules will have canonical name "x". In this case, issue an
error message, and discard the docs from the second item.
(Otherwise, there would be 2 problems: first, we'd try to merge the
docs of these two modules; and second, we wouldn't have unique names
for them, so we'd end up overwriting the doc files of one with the
doc files of the other.)

- Dropped old stylesheets.

- Typo fixed

- Added HTML manual generation

- Adding user manual.
A chapter on reST and Javadoc is required. To be done soon.

- rst2html to be used to produce other web pages other than the doctest.
- added support for '.. python::' directive
- added support for epydoc api directive
- the stylesheet is linked with the path properly mangled.

- Added customized css (a more generic version of the one used by doctests)
- Docutils base CSS updated.

- A pair of typo fixed.

- Generated HTML pages description updated.

- Fixed docstrings so they correctly link to the Epydoc API.
Currently it is required to use `register_canonical_role()` instead of
`register_local_role()` in `xlink.create_api_role()`