Handle TypeError on parsing JSON.

In Tornado, request.body is normally a string, but it can be a
concurrent.Future on streaming requests. This means we also have to
handle TypeErrors on parsing JSON.
Bump dev version and update changelog
Merge branch 'jmcarp-dev' into dev
Bump version and update changelog
Bump dev version
Allow use argument to be a list of callables
Add example usage with Flask-RESTFul

closes #20
Update contributing docs
Don't catch all generic exceptions

Only handle ValidationErrors

fixes #22
No need to call iter on dict.items
Group all Arg tests in a test class
Update changelog
Test that "source" name is passed to custom target handlers
Add a short-lived cache for storing processed request bodies

resolves #23
Store decoded json body in cache rather than an attribute

No need to parse JSON body on every call to parse
Removes temporary data on each parse
Make _parse_json_body a function rather than a method
Update changelog
Merge branch 'feat/cache' into dev
Initial draft of type validation
Use types instead of strings in json types dict. Fix check for null