Switch to using my work directory for submit dirs
Expand ~ to the user home dir for submit_dir
Add more stats for each chip and output them to a json file for now.
Add measurements of PSF shape, size
Add measurements of rho stats for each chip.
Pull out the code to build the exposure catalog into a separate script.
Updates for v4

- Change FEW_STARS to 20 rather than 50
- Change MANy_STARS to 50% of total rather than 500.
- Keep track of findstars and psfex failures, and flag them directly.
- When findstars fails, run again with verbose=2 so I can look to see
  what happened.
Slight simplification to setup_output to remove unnecessary flags
typo
Forgot to actually run the second pass findstars command.
Don't trust existing files.

This seems to have been the problem with at least some of the findstars
errors.  Probably when I stopped jobs partway, the files were made, but
they are corrupt.  So better to always assume that we need to remake all
files.
Simplify codes to use a default exp_match that is what we always use.
Add in calculation of rho for full exposures.
Add workaround for some bad DES images that don't read correctly.
Check for PSFEx files that don't parse correctly and mask them.
Add routine to plot the rho stats