Python API documentation generation tool Code

- 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()`

- Don't load duplicate entries in the URL generators.

- Always using the registered name to get the resolver, so it can work
as default role too.

- Using Epydoc logger to report index file parsing errors.
- More robust index file parsing.