Only reparse for the case of all the text deleted if we're on the first line.
Add the option to use line by line parsing, which will only parse small sections of the document before highlighting, resulting in much more responsive highlighting.  Also disable visible only highlighting by default (and rename), since it doesn't play well with codemirror's token buffer (it generates tokens for more than just the visible area, so that scrolling is smoother).
1.2.0
1.2.1