Remove FUNCTION argument, useless.

Because it was highly SBCL specific, so it needs to be reorganized,
either by IOLIB's multiplexing, or using threads.
Add postprocessing options, automatic render path.

Which now allows the user to quickly say what they want and otherwise
still retains the old explicit conventions.

Conversion tools and compiler options still need refinement, but it
works fine for simple cases.
Fix the command line for dvips.

Now we can actually supply more arguments if we need to.
Fix issue with conflicting inputs.

I.e. if we calculate the output format, don't error out.
Explain the new stuff in the README file.