Add support for hinting function types.

When in a function call, display the function type instead of the normal hints.  This only happens when nothing has been entered by the user - if the user starts typing, then we switch back to the normal hints based on what the user has typed.

This also requires a new version of CodeMirror that brackets has not updated to.  The old hints continue to work without the new version, but the function types will only work once codemirror is updated.