This adds real command line handling to 'hyc' for issue #256
This fix catches missing/unreadable files and prints a nice
error message instead of a nasty stack trace when trying to
compile a non-existent file.
Also add this non-existent file check to hy to prevent the
current stack trace from something like "hy foobarbaz" when
"foobarbaz" doesn't exist.
also changes the failure return value to 2 to match Python.
d960dc963f