luav: add script ala pipv/brewv

This builds a sandbox lua using a useful gist from Jim Whitehead to bootstrap
luarocks availability, installs vert into this sandbox, uses vert to set up
the requested lua environment, and runs luarocks to install the specified
rocks, and then adds wrappers to $XDG_DATA_HOME/../bin which run the
scripts/binaries in the luaenv.

Signed-off-by: Christopher Larson <kergoth@gmail.com>