Make addMessage chainable.

According to the docs in the "Craft yours!" section the addMessage
method is chainable. This should restore this feature.
Merge pull request #581 from zerok/fix/addMessage-chainable

Make addMessage chainable.
- fixed `asyncIsValid()` and `asyncValidate()` API to support `force` option
- added more parsley.remote tests
Corrected grammar, fixed markdown, fixed spelling.
Merge pull request #583 from bool-dev/patch-1

Corrected grammar, fixed markdown, fixed spelling.
- added parsley remote options tests
- added test to ensure errors container is not appened if field is excluded. Closes #553
- RC5
Merge branch 'master' into gh-pages