This makes getStateAfter without an argument work as intended

Closes #149

These had been broken since the theme system overhaul.

The code was leaving off the last one or two lines when selecting
multiple lines and pressing tab.

So that we don't create extra garbage for each escape

Contributed by Dror Ben-Gai

Courtesy of Łukasz Frankowski

Closes #138

This would be visible in the activeline demo, where the colored line would get
shorter and shorter for each display update.

Also fixes a bug with computing the max width and height for placing the widget

Can be one of 'below' (default), 'over', or 'fit', and controls the way
the widget is positioned in relation to the given character position.
'fit' means CodeMirror does its best to keep the widget inside the current
dimensions of the editor.

To help external code easily determine which mode a getTokenAt token is in