userland #66

Now returns correct codes on exit(). Good run returns
EX_OK(0), bad command line parameters return ES_USAGE(64),
camera failure EX_SOFTWARE(70).

Codes from sysexits.h were used.

Doesn't yet implement the 'strict' option suggested by a
contributor on github, I'm not convinced that's all that
necessary.

Updates docs files to include all recent changes.