Updated plugin for TinyMCE 4

I updated support for TinyMCE 4 and its updated initialization.

Also updated documentation, demo, and spec to work, although I did not rewrite the already-commented out spec for those to pass.

The directive works as it did before, with any options you would like to pass on to TinyMCE to be passed with an attribute value - here is an example:

__HTML__

    <form method="post">
        <textarea ui-tinymce="tinymceOptions" ng-model="tinymce"></textarea>
    </form>

__JS__

    $scope.tinymceOptions = {
        setup:  function (ed) {
            ed.on('keypress', function (e) {
                console.log('keypress event');
                console.log(e);
            });
        }
    };

The value saved in `$scope.tinymce` is the HTML structure and text generated by TinyMCE.

For example __bold text__ would be stored as `<strong>bold text</strong>` in `$scope.tinymce`.

Potential issue:

I have not been able to test/verify whether my rewrite of the `change` or `setContent` binds are correct.