Cache system and local font directory construction to avoid repeated string ops and calls to system funcs

Add variant of unpackVolumeFaces that accepts a char* buffer to avoid additional malloc for input/output

Add variants of unzip_llsd that accept a char* buffer and do not allocate an additional input copy buffer

following promotion of DRTVWR-525

Port MoonWalk feature. Fix #52.

Closes #52

See merge request alchemy/alchemy-next!21

Add support for multiple overlays in the same linkset (and support permanence in @setoverlay restrictions that aren't currently active)

CATZ-590: Unpredictable results occur when both @setsphere and @setoverlay are set by the same object