add test cases for VCSRepo.tip()
implement VCSRepo.tip()
add test case and functionality for HEAD
documentation improvements

- move VCSRepo documentation into anyvcs.rst
- delete anyvcs.common.rst
- add more flowing text for readability
move __version__ into anyvcs/version.py

This is probably a good idea for down the line stuff. This way __init__.py is
free to import stuff as it pleases and won't run into any 'chicken and egg'
issues with setuptools.
read version information from anyvcs/conf.py
reorganize and rename git, hg, svn specific pages

All the pages are linked directly by the index so the documentation is less
deep. The section headers are English instead of module names.
add unit test exposing issue #47
fix issue #47: use fullpath instead of name in HgRepo._cat()
expose issue #46 in unit tests
fix issue #46 by making bookmark_rx handle negative revs
fix naming conventions and HgBasicTest.test_heads
Merge pull request #44 from OEP/feature/tip

Unit tests and implementation for VCSRepo.tip()
Merge pull request #45 from OEP/feature/doc-improvements

documentation improvements
Merge pull request #48 from OEP/feature/iss47

fix issue #47
Merge pull request #49 from OEP/feature/iss46

fix issue #46 by handling negative revs in anyvcs.hg.bookmarks_rx