Add --exclude option
Discard images taken in any of the given --exclude filters
Add Bash completion for --exclude
Make --filter and --exclude incompatible
Add --exclude option

This is the opposite of --filter: it allows us to specify one or more
photometric filters in which photometry will not be done — those FITS
images taken in any of them are discarded. The --exclude option is
incompatible with --filter, so they cannot be used at the same time.

This merges branch 'add-exclude-option'