Send correctly-formatted If-None-Match header

Closes #43
Merge branch 'mattly/43-if-none-match'
bump version to 0.6.1
update readme notes for 0.6.1
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
leftovers from previous
tests in one place
KV#last_request_time