WIP HMAC authentication view
Update the base ApplicationException with custom headers

Also update the exception_handler to set those headers on errors.
Updated HMAC with working implementation
Tests for HMAC authentication / failure states
Added docs and cemented the public API for HMACView
Index the authorization header as it should always be included
Added docs for authentication with HMAC signed requests
Link in the table of contents
Reworded HMAC definition
Merge pull request #39 from ox-it/authentication-hmac

HMAC authentication view
Updated to double backticks for literal markup
Merge branch 'master' into places-geoposition

* master:
  Updated to double backticks for literal markup
  Reworded HMAC definition
  Link in the table of contents
  Added docs for authentication with HMAC signed requests
  Index the authorization header as it should always be included
  Added docs and cemented the public API for HMACView
  Tests for HMAC authentication / failure states
  Updated HMAC with working implementation
  Update the base ApplicationException with custom headers
  WIP HMAC authentication view