Fixes bugs with attaching featured images to posts

This commit fixes two bugs in `WP_JSON_Media::attachThubmnail()`.

    - `attachThumbnail()` should dp nothing if `$update` is false since
    the post ID is needed.
    - The post ID must be fetched from the `$post` array.
Test all versions of PHP, with WP trunk
Add documentation on testing/developing
Don't check for IXR_Error
Remove IXR includes
Change to WP official git mirror
Just copy the files instead of cloning the repo again (this way it even works on branches tests, I think)
Merge pull request #80 from osiux/fix-travis-integration

Fix travis integration
Change function semiCamelCase names to underscore_case on lib/
Change function semiCamelCase names to underscore_case on docs/
Change function semiCamelCase names to underscore_case on plugin files.
Use name of plugin on deprecated notice.
Removed test support for multiple WP versions.
Merge pull request #84 from tierra/continue-unit-testing-structure

Removed test support for multiple WP versions.
#85 - added timezone parameter to WP_JSON_DateTime::createFromFormat() in parse_date method.
Provide default timezone fallback in WP_JSON_DateTime::createFromFormat().
Added class comment and code formatting fixes to WP_JSON_DateTime class.
WP_JSON_CustomPostType __construct() requires a param of type WP_JSON_ResponseHandler. This needs to be documented. It's not clear how to write getPost, editPost, getPosts, and newPost methods mentioned in the MyPlugin_API_MyType class: I added a sentence explaining where you could start with these.
Merge pull request #88 from tlovett1/master
Merge pull request #87 from rachelbaker/issue-85

#85 - added timezone parameter to WP_JSON_DateTime::createFromFormat()