share the same scope among several routes
only look for keys that could have been created by the limiter
helper function for building app / extension
implementation for shared limits (#8)
fix docs to use shared_limit
remove auto generated scope names.

This doesn't work for multiple app instances running
since each instance will generate a new UUID for the
same shared_limit.
Merge pull request #8 from g-p-g/master

Share limits between several routes