Add FFI for Lua

Nearly full support for standard API
Partial support for debug API
Minimal support for aux API
Add simple crate file
Correct FFI function definitions and add constants

Add missing constants, and declarations for lua_load,
lua_absindex, lua_arith, lua_atpanic, and lua_iscfunction
Add basic safe wrapper

Implement simple stack operations, pushing and pulling values between
Lua and Rust
Add appropriate license
Add build and use sections to readme file
Remove references to non-function lua_pop

Replace usage with lua_settop
Modify rust-lua to build with rustpkg
Correct FFI callback types and add constants

Correct extern fn pointers, and add Lua's pseudo-index constants
Modify spacing style

Replace tabs with space indentation