Add PUT and DELETE methods to http plugin

Supporting a full REST pattern requires these verbs. using 'delete' as a property name can cause issues in IE7<, without quotes, so to avoid the issue I used 'remove' as the method name. Required that it be accessed with the indexer would allow the use of 'delete' as the method name, but this is cumbersome.

Another thing to note is that DELETE expects a URL like GET, not a body like POST/PUT. There seems to be some agreement that, while allowed, [DELETE bodies should be ignored](http://stackoverflow.com/questions/299628/is-an-entity-body-allowed-for-an-http-delete-request).