This extends the diff driver parser to support multiline driver
definitions along with ! prefixing for negated matches.  This
brings the driver function pattern parsing in line with core Git.

This also adds an internal table of driver definitions and a
fallback code path that will look in that table for diff drivers
that are set with attributes without having a definition in the
config file.  Right now, I just populated the table with a kind
of simple HTML definition that is similar to the core Git def.