Add support for Lua chunks

[davydog187]

Adds chunk support, which allows users to precompile Lua statements and then execute them later, as opposed re-parsing and code generating at eval time. We achieve this with the following two features

1. The ability to return chunks from the Lua sigil with the 'c' modifier

~LUA"""
print("hello world")
"""c

2. The ability to load and evaluate chunks

{[4], _} = Lua.eval!(~LUA[return 2 + 2]c)

Closes #35