Missing memecahcded commands implementation

Hi Nikolay,
This is kind of a bold code change, tests rewritten and *Makefile* replaced in order to make *aiomcache* look more similar to other *aio-libs*. Feature summary:

- added new commands: *incr*, *decr*, *touch*, *add*, *replace*, *append*, *prepend*, *flush_all*
-  test moved to unittests, and could be invoked with runtests.py script
- coverage 92%
-  fixed travis-ci

Please review.