output catalogues with .crtf format

[PaulHancock]

Aegean can output catalogues in the following formats:

Extension |     Description       | Supported?
ann        Kvis annotation          False
csv        Comma separated values   True
db         Sqlite3 database         True
fits       FITS Binary Table        True
html       HTML table               True
reg        DS9 regions file         True
sqlite     Sqlite3 database         True
tab        tabe separated values    True
tex        LaTeX table format       True
vot        VO-Table                 True
xml        VO-Table                 True

It would be nice to also support CASA Region Text Format with extension .crtf, (docs).

[PaulHancock]

crtf format doesn't seem to support pixel coordinates which means that I cannot (easily) write pixel boundaries like is done with ds9.