Add support for MEMCACHED_BEHAVIOR_TCP_KEEPALIVE

Change-Id: I7b8bcd29f3b137a6220351324a227c9094c49899
Add support for MEMCACHED_CALLBACK_PREFIX_KEY in behaviors.

Change-Id: I782a3231fc770b7f24993541144d3131c22ffe74
typofix README
Merge pull request #77 from myYearbook/1.2.2-behaviors

MEMCACHED_BEHAVIOR_TCP_KEEPALIVE and MEMCACHED_CALLBACK_PREFIX_KEY
Merge branch 'master' of github.com:lericson/pylibmc
Add touch support
add thanks
Always return two-tuple from gets
Add hash method
Update name for prefix_key to namespace
Add documentation for gets, cas

Closes #91
Add tcp_keepalive to behavior test
Add touch support
Added tests and documentation for touch support
Consolidate tests for client to one location

test_cmemcached.py is borrowed from another library to make sure its test passes on our codebase. It should not be used to add tests.
Merge pull request #94 from kjw1/master

This is done by incorporating changes from @rbranson.

@kjw1, @rbranson added to list of authors.
Add benchmarker utility
Reorganize directory layout
Add datastructure for get_multi requests

The idea is to use pylibmc_mget_req for an upcoming get_multi_async
feature.
Mention that pylibmc.Client is *not* threadsafe like python-memcached