Add markdown to README.
give md extension to README.
Minor reworking of README content.
Merge pull request #67 from jasonbaldridge/master

README update
FeatureVector moved to math
move optimize
got rid of futures from PQN. Those operations are usually too fast to matter
these need to stay in learn.
don't need concurrent ep.
don't need maxentobjective, since I never tested it.
removing semicolons
Merge branch 'reorg': all the non-learning parts of learn are
in Math now. Or deleted.