Bumps version to 0.5a1.
Increases the unit test connection read timeout again for Travis CI.
Fixes --continue option to be grouped.
Fixes finish time formatting.
Moves readme from Markdown to RST.

This allows proper rendering in PyPI.
Fixes keep alive not working. Implements --no-http-keep-alive.
Adds cache module.
Implements dns caching.
Implements --rotate-dns.
Backports functools.total_ordering.
Fixes Resolver to use global cache.
Changes all IOLoop.instance() to IOLoop.current().
Adds more debug statements.
Ensures unit test http server is fully started up.
Fixes Resolver to properly cache empty results.
Increases unit test timeout to 30 to account for resolver delay.
Fixes backport/functools.py str issue in 3to2.
Updates backport.py with latest version 727027eadace.
http.py: Adds active property to Connection. More debug statements.
Uses concurrent unit test http server. Increases writer_test timeout.