Add support for Pygments filters in codehilite

[jvoisin]

Pygments supports filters, and some of them like TokenMergeFilter could significantly help with reducing the size of the produced html on some pathological cases.

[waylan]

In version 3.3 we made some significant updates to the codehilite extension to allow most any arbitrary option to be set for Pygments. In fact, as the documentation states (at the bottom of the Usage section):

All other options are accepted and passed on to Pygments’ lexer and formatter. Therefore, valid options include any options which are accepted by the html formatter or whichever lexer the code’s language uses. Invalid options are ignored without error.

Of course, that requires the filter to be able to be passed to the Lexer on initialization. While Pygments' documentation seems to suggest that you can only add filters by calling the add_filter method from an instance of the lexer, you can in fact pass filters in on initialization.

Therefore, you can do this:

markdown.markdown(src, extensions=[CodeHiliteExtension(filters=[TokenMergeFilter()])])