A place for Lua module sources

[Marc Balmer <mbalmer%NetBSD.org@localhost>]

All of Lua currently resides in external/mit/lua.  For now that is the
library and the lua/luac binaries.

We should also define a location in the source hierarchy where we can
place source code for modules.  Since all modules I stumbled over so far
are under the same MIT license as Lua itself, I suggest to place them
under the external/mit/lua directory as well.  Maybe under
external/mit/lua/modules/<name_of_module>/.

My idea is to import a small set of modules that interface functionality
in base:

- posix: General POSIX functions
- ldap: Interfacing LDAP
- gpio: GPIO access
- netbsd: Very specific NetBSD functionality not found in posix or any
other module (e.g. accessing sysctls)

Opinions on the path for modules?  Or on the modules themselves?