rfc: optimization tips for luajit, 5.2, and other implementations

[David Manura <dm.lua@...>]

The OptimisationTips [1] wiki page lists various tips for
restructuring Lua code to perform optimally, but it is primarily
geared toward the standard Lua 5.1 VM, ignoring other Lua
implementations [2].  These guidelines remain largely the same in the
standard Lua 5.2 VM bar a few things like lightweight C functions and
Lua function caching.  To a larger degree, however, many of these
guidelines/assumptions may be completely invalid in LuaJIT and
JAVA/.NET/JavaScript Lua implementations.  So, I think it would be
worthwhile to document the performance profiles of these other
implementations to better assist authors targeting multiple VMs.

[1] http://lua-users.org/wiki/OptimisationTips
[2] http://lua-users.org/wiki/LuaImplementations