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
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()
Move from wp-json.php/ to wp-json/
Use `wp-json/` in documentation
Merge pull request #96 from WP-API/drop-php-suffix

Drop PHP suffix from URLs
Merge pull request #77 from WP-API/remove-ixr-references

Remove IXR references
Merge branch 'master' into continue-unit-testing-structure
Merge pull request #55 from Webbgaraget/master

Fixes bugs with attaching featured images to posts
Shallow-clone WP for testing

Props @osiux