Parse options in htools.hs, not in each program

This patch moves the call to getArgs/parseOpts into htools.hs, as
opposed to the current situation where htools.hs only calls the main
file of each program, which in turn calls these two functions.

By doing it only once we remove some duplicate code and we also export
each program's options, which allows us to test some common behaviour
in the future.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>