Implement 5.1 compatibility layer in Ravi

[dibyendumajumdar]

I would like to support running 5.1 scripts in Ravi, hence plan to add a compatibility layer for 5.1.

[dibyendumajumdar]

setfenv/getfenv emulation. Here are links to some notes on what needs doing:

http://lua-users.org/lists/lua-l/2010-06/msg00313.html
http://lua-users.org/lists/lua-l/2011-05/msg00124.html
https://stevedonovan.github.io/Penlight/api/source/compat.lua.html
http://lua-users.org/lists/lua-l/2010-02/msg00753.html
http://www.corsix.org/content/look-lua-52-work3

[dibyendumajumdar]

• setfenv/getfenv
• newproxy
• gcinfo