new routine to parse header card
add FITSRecord, FITSCard.

FITSHDR now uses FITSRecord internally instead of raw dicts.  This
should be transparent since FITSRecord inherits from dict.

Also incorporate the parse_card function from the C code.
pull in FITSRecord and FITSCard
updated changelog
always convert to FITSRecord
better error message
account specially for COMMENT because cfitsio treats first four of those specially
fix bug with empty strings
simplify fits record handling from cards
some docs
some docs
some docs
some docs
fixed a few function declarations that were not static
move extra funcs into pywrap so we can make them static
remove unused files
removed unused files
formatting
docs in changelog
update existing keys on add_record or setitem