code for purge if-match
update docs for purge, if-match
Client#post uses auto-generated keys
update readme notes for WIP
Merge branches 'mattly/52-kv-post' and 'mattly/40-purge-if-match'
update Readme notes for 0.6.2
version 0.6.2
Orchestrate::Application constructor

baby steps
Orchestrate::Collection
Collection#destroy!
Collection#[]
KeyValue#load / #initialize WIP
Collection#[] returns nil on NotFound
KeyValue#[], #[]=
KeyValue#save handles failure cases
KeyValue#save!
refactor common errors to helper
resolve test class name conflict
KeyValue#destroy, #destroy!
KV persistence tests extracted