Use PyStemmer instead of PorterStemmer.

PorterStemmer consumes a lot of time. So use PyStemmer
<http://sf.net/projects/pystemmer/> implemented in C.
Don't use publish_parts to avoid building OptionParser many times.
Use porterstemmer instead of PyStemmer.
tune traversing. 29s->24s
merge to master
merge with http://bitbucket.org/methane/sphinx-speedup/
merge with 0.6
merge with 0.6
merge with pv/sphinx-work
Fix a few stylistic nits.
Fix a few stylistic things, and add docs for autosummary_generate.
Add changelog entry.
Fix the test suite.
autosummary: make information messages prettier
autosummary: refactor generate.get_documented*

Refactor the RST parsing functions by dropping parts that are not needed
by the autosummary extension. Also fix some bugs (handling of duplicate
entries and parsing of the :toctree: option).
autosummary: fix bug in importing top-level modules
Allow searching for object names including the module name, like ``sys.argv``.
Ignore stopwords and numbers in search.
autosummary: fix typo in a regexp
Make doctest block definition clearer.