Feature/compressing codecs

[lloydmeta]

This is a much less ambitious version of #50 with the sole aim of migrating to using SpyMemcached's Transcoder as a parent class of Codec.

The main goal is to get parity with other Spymemcached-using systems as well as compression once the data size goes above a certain threshold.

[alexandru]

@lloydmeta doesn't look bad 👍