Add Quake II MD2 model format (#619)

* Add files via upload

* put it in the wrong place

* Add QuakeII MD2

* Frame names are null-terminated

* Tweak description

* Delete md2.ksy

* Expand docs and incorporate feedback

Added documentation on standard animation frames. Renamed to quake2_md2. Used list doc-ref and `strz`.

* Markdownify table

* Add animation start frames as an enum

* Prettify table as preformatted ASCII

* Use value instances for anim name/start/count map

* Apply suggestions from code review

Co-authored-by: Petr Pučil <[email protected]>

* Apply suggested punctuation

* Apply suggestions from code review

Co-authored-by: Petr Pučil <[email protected]>

* Suggested changes (metadata, gl_cmds)

* anorms_table value instance

* Move anorms doc-ref to table def

* Apply suggestions from code review

Co-authored-by: Petr Pučil <[email protected]>

* doc indexes -> indices

* Mention `normal` and u,v -> s,t

* Apply suggested sq bracket format

Co-authored-by: Petr Pučil <[email protected]>

* Trim trailing whitespace

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Co-authored-by: Petr Pučil <[email protected]>