Rename 'RequestIndentity' to 'RequestIdentity'
Add overridable method to compute store key
Refactor code to increase readability

- Move whitelist checking to separate method
- Short-circut large control statements (if and foreach in SendAsync)
Use member ThrottlePolicy instead of passing it around
Fix endpoint throttling check
Combine ComputeHash and ComputeStoreKey methods into ComputeThrottleKey
Merge pull request #5 from omar/master

Allow override of throttle key computation