- Fix the literals formatting in computePixelToDistortedPixel.
- Add cross references and other minor syntax improvements.

These objects were generating doctree not found errors (See DM-15056). I
think this is because some code was filtering out lsst.geom APIs, but
not fully. Manually filtering them in the automodapi directive solves
the problem for now.

This is what we want, design-wise.

This adds the FITS header reference page into the right directory. This
also sets up the standardized structure of the lsst.afw.image module
homepage.

This will be easier to maintain than the drawn tables.

This makes the table a bit easier to read since it allows the
description column to be wider. The accessor is still quite apparent
thanks to its formatting, and role as a link to the API reference.

LTV1 and LTV2 no longer hold XY0 (those keywords are still written,
though we probably should not mention that, as LSST code never reads
them). XY0 is now encoded as WCS "A" using the following keywords:

CRPIX[12]A = 1
CRVAL[12]A = xy0
CTYPE[12]A = "LINEAR"
CUNIT[12]A = "PIXEL"

where [12] means 1 or 2, so CRPIX1 = CRPIX2 = 1, CRVAL1A = xy0[0],
CRVAL2A = xy0[1], etc.

This moves the Footprint.rst topic into the right place, and deletes the
older doc/detection directory.

No longer needed with stack-docs and package-docs command line tools.