rpl-mode: fontify the header specially

First of all, did you know the header ends with ";"?  I sure missed that
one...

If the header doesn't match the magic header string (like, if you forget
the ";"), it matches the "this is not a proper port" test and hilights
as an error.  If it matches, it gets hilighted as a preprocessor word.
rpl-mode: shortcut function to insert a US-centric header

Create the header and set transform all special, degrees angles, and
dot-decimal point.  Maybe this should be modified at some point to be
smart about localization?

Also, this header should affect the mode line and have quick change
shortcuts somehow... ...