Fix the StackPolicyURL param.
Updating models to latest versions.
Bumping version to 0.28.0
Merge branch 'release-0.28.0' into develop

* release-0.28.0:
  Bumping version to 0.28.0
  Updating models to latest versions.
Update translator to denormalize waiter config
Initial commit of waiters
Parse JSON response based on the service type, not content type

Fixes issue #136 as well as fixes aws/aws-cli#553.
Pull in waiter configs to group by acceptor types

Rather than success_* and failure_*, move them into a dictionary.
This cleaned up the implementation.
Merge branch 'fix-issue-136' into develop

* fix-issue-136:
  Parse JSON response based on the service type, not content type
Add waiter configs to services
Add copyright to waiter.py
Add docstrings/comments for waiters
Fix typos
Merge branch 'waiters' into develop

* waiters:
  Fix typos
  Add docstrings/comments for waiters
  Add copyright to waiter.py
  Add waiter configs to services
  Pull in waiter configs to group by acceptor types
  Initial commit of waiters
  Update translator to denormalize waiter config
Bump jmespath dep to 0.2.1
Update models to the latest version
Add support for new cn-north-1 region
Merge branch 'cn-north-1' into release-0.29.0
Add docs for cloudfront model
Bumping version to 0.29.0