psFits stuff

[Paul Price]

We need to make clear that reads and writes operate only on the current extension.

We need to specify a "Create template header" (can set BITPIX, NAXIS, NAXIS[12]
from a psImage):
psMetadata *psFitsCreateHeaderFromImage(psMetadata *header, psImage *image, int
naxis3);
psMetadata *psFitsCreateHeaderFromValues(psMetadata *header, int bitpix, int
naxis1, int naxis2, int naxis3);

I should be able to read in a header from a FITS image, muck with the pixels
(changing naxis[12] and bitpix) and then input that header into
psFitsCreateHeaderFromImage and get the correct header without losing any of the
other precious header keywords.

[Paul Price]

psFits has been reworked.