Adds Quicklisp support to Common Lisp.

[remexre]

Would it also make sense to change --script to --load in the run.command? --script disables the interactive debugger and the REPL; it's intended for usage in the shebang of a script run by someone who's not necessarily a Lisp developer.

[remexre]

Hm, stage2 (and probably other stages) don't properly escape language names. Would it be preferable to throw a bunch of quotes around the scripts, or to change the name field to common-lisp or similar?

[remexre]

Oh, the run.command needs to be changed regardless: --script won't load things in the init-files, so loads neither Quicklisp nor ASDF.

[dan-stowell]

Good afternoon @remexre ! You've probably noticed by now that we've been slow to merge community PRs on polygott. We've decided to focus on giving Repl.it a stable foundation instead of adding features and updating languages. Once we and our community feel comfortable with Repl.it's overall stability, we'll give this change another look. Thank you for contributing!