Add page about garbage collection

A general garbage collection page seems useful. This could explain what garbage collection is and give an overview of the different possible approaches and common issues. Particularly useful to people who haven't programmed in dynamic languages much/at all. This could also be a place to talk in very general terms about how different lisps (Not different common lisp implementations) handle garbage collection.

[vipermark7]

Has anything been done about this? If not, how can I help?