Upgrade dependency pyramid_metrics to 0.1.5
Implement cache inhibition in Redis client
Implement cache inhibition in cache manager
Use CacheDisabled instead of InhibitCaching
Merge pull request #11 from pior/feature-inhibit-cache

Cache can be inhibited by setting master key to 'off'
Make new CacheResult object

This object allows the view decorator to add HTTP headers to the
response such as ETag and cache information.
Replace MD5 with SHA1

Change the cache key hashing algorithm from MD5 to SHA1.