Fix jsonp content-type response header

Incorrectly sends application/json rather than application/javascript on a jsonp request which breaks strict mime handling. In response to error: Refused to execute script from '...url...' because its MIME type ('application/json') is not executable, and strict MIME type checking is enabled.
post 'parent' value should be null rather than zero if unset

Having a field be either an integer or a nested object makes parsing more complicated. Furthermore, knowing that a parent ID of "0" means that a post has no parent is WordPress inside knowledge that should not leak through the API.
Add license.txt file with license terms for #384
Merge pull request #391 from maxcutler/patch-2

post 'parent' value should be null rather than zero if unset
Merge pull request #393 from WP-API/license

Add license.txt file with license terms for #384
Update README.md

Update Testing procedures to include the running provision step before running the testing suite
Offload WordPress installation to bash script so it can be reused
Run tests against single site and multisite
Support for running tests in a few ways
Change our plugin activation test
Merge pull request #396 from ironpaperweight/patch-1

Update README.md to include provision step for testing suite.
Improve tests for multisite
Made clear that WP.com API was available as part of JetPack

Also, added link to codex page for XML-RPC API.
Minor wrapping and grammar fix.
Check that the JSONP callback is a string first

If you pass in an array, this would cause a warning.

Props @ircrash
Resolves #409. Now matches dashes in addition to alphanumeric and _ characters
Refactored regex to use \w again and simply add - to the group
Updated Tests to check for the updated keys, moved old keys to deprecated list
Or maybe they shouldn't be listed in deprecated and checked
Fixed deprecated keys... to use the newer route