remove unused statistics
remove statistics, patch SASLMemcached

Memcached on heroku does not support value > 1M.

This spread those values among multiple keys
use custom cache for memecached
fix import for sasl
update requirement

remove explicit version number,
move to flask-cache dev
Merge pull request #47 from Carreau/split-cache

Split cache

Write a memcache client which is able to store big values on multiple keys.