Add Support for Functions

[hjdivad]

local fn_info = debug.getinfo(fn, 's')
fn_info.source --=> @.repl.lua
fn_info.linedefined --=> 6
fn_info.lastlinedefined --=> 8
fn_info.nparams --=> 2
fn_info.isvararg --=> false
fn_info.nups --=> 1

This allows us to add support for functions defined outside of stdin. For a
REPL usecase, this means sending loadfile(<file>)() to the REPL instead of
the lines themselves.

nups ("number of upvalues") can be used to see if the function requires a closure.

With this information we can support functions that:

1. Do not require closures (i.e. nups == 0)
2. Are defined somewhere other than stdin

[hjdivad]

It's possible that debug.getupvalue makes even closure functions possible, especially for the limited use case of lua code that all lives in a repl.lua that is sent to a REPL.