added ipac ascii writer
attempted to massage ipac writer to work with astropy, but it was a
failure
reorganized; writer works now but has inconsistently formatter header.
Tried adding ipac metadata parser, but no luck yet - where does the
BaseReader class pass metadata to the Table?
the column header width was a bug; fixed
corrected metadata handling (probably relies on #683)
attempted to fix ipac writer to use FixedWidth stuff, but it breaks a
lot of other tests now
Merge branch 'ipacwriter' of github.com:keflavich/astropy into ipacwriter

Conflicts:
	astropy/io/ascii/ipac.py