Support Custom Post Types

[kadamwhite]

Before this is released, we need to have support for custom post types.

Alternative syntaxes under consideration:

Generic types handled by a single types endpoint handler:

var wp = new WP( options );

wp.types( 'cpt_event_listing' ).then(/* ... */);

Create custom endpoint handlers with a registerType utility method (see #7):

var wp = new WP( options );
wp.eventListings = wp.registerPostType( 'cpt_event_listing' );

wp.eventListings().get().then(/* ... */);

In either case, the type method would wrap .posts() but would set properties to specify a type query parameter to filter results.

@carldanley, I'm particularly interested in your opinion here since you're familiar with the WP internals

[kadamwhite]

@rmccue +1'd my proposed pairing of wp.posts().types( 'some_cpt' ) and wp.myType = wp.registerType( 'my_cpt' ) as our custom post type methods of choice. This issue will be closed out by #52.

[kadamwhite]

Merged #52: closing.