bin/hy2py: Add a bunch of command-line options

The hy2py tool has been very useful for me, but most of the time, it's
only a part of its output that one is interested in. The whole output,
with source code, AST and python code together is one big monstrosity.
So instead of printing all that, lets have a few handy command-line
options to control which part gets printed.

By default, only the generated python source is, as that's what the name
of the tool implies.

Also, don't run it. That's what hy is for.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>