When using file-level compression, allow setting compression parameters

[dstndstn]

In the legacypipe code, we use mem:// files very extensively -- this allows us to do in-memory checksums before writing to disk.

We also use compression extensively, which we set at the file level via extended filename syntax - eg we create files like

fits = fitsio.FITS('mem://[compress R 100,100; qz -1e-4]', 'rw')

However, we find that when doing this, when you go to write an image HDU, the compression parameters don't get passed through because compress= is not set.

This patch fixes that.

Test case: these two files should get the same ZDITHER0 set.

import numpy as np
import fitsio
A = ((1+np.arange(10000)) * 0.1).astype(np.float32)

fitsio.write('dither1.fits', A.copy(), dither_seed='checksum', compress='RICE', qlevel=1e-4,
             tile_dims=100, clobber=True)
hdr = fitsio.read_header('dither1.fits', ext=1)
print('File #1: ZDITHER0:', hdr['ZDITHER0'])

fits = fitsio.FITS('mem://[compress R 100,100; qz -1e-4]', 'rw')
fits.write(A.copy(), dither_seed='checksum')
data = fits.read_raw()
fits.close()
f = open('dither2.fits', 'wb')
f.write(data)
f.close()
hdr = fitsio.read_header('dither2.fits', ext=1)
print('File #2: ZDITHER0:', hdr['ZDITHER0'])

[esheldon]

Thanks Dustin. Can you add a unit test for this one?

[beckermr]

Thank you!