Add dumpvar & exportvar

[Sainan]

The original goal was table.dump (#337), but I ended up being a bit inspired by PHP's var_dump and var_export.

local t = {
	[1] = "a",
	[2] = "b",
	["a"] = 1,
	["b"] = 2,
	["t"] = {
		["deez"] = "nuts"
	}
}
t["r"] = t
print(dumpvar(t))

Possible output:

{
        [1] = "a",
        [2] = "b",
        ["a"] = 1,
        ["b"] = 2,
        ["r"] = *RECURSION*,
        ["t"] = {
                ["deez"] = "nuts",
        },
}

---

TODO:

• Quote strings
• Add exportvar that guarantees valid Lua code, so errors on recursion