generated binaries show usage when given -h/--help

[badmutex]

This is for #6

This change allows generated binaries to show usage info upon consumption of -h, --help (and -? incidentally).

Tested

• on Ubuntu 16.04 with make test

Example

$ ./bin/trck -c test/tr/test_field_name.tr
$ ./matcher-traildb --help
Usage: ./matcher-traildb [OPTIONS] TRAILDB [TRAILDB...]

OPTIONS:
  -p  --params        PARAMS
  -o  --output-format FORMAT
  -f  --filter        FILTER
  -w  --window-file   FILE

[CLAassistant]

All committers have signed the CLA.

[oavdeev]

May be nitpicking, but I thought EX_USAGE is intended for the case when the binary received incorrect arguments

[badmutex]

True. The case '?' clause for unhandled arguments will fall through to the case 'h'.
My thought is that invocations that result in the usage printed indicate bad arguments and explicitly asking for the usage is a special case.