Stop hy script from eating all CL args

This updates the bin/hy script to peel out the args it needs and then reset sys.argv (like Python) before calling the a script to run. 

Includes a little example hy/argparse script and added some tests to run this script. 

I wasn't sure where to put the argparse_ex.hy script that the test needs, so I dropped it into the same directory as the test. It isn't enough of an argparse example to go into "eg".