V N 5209271db3 Lua: add variables metatable
The implementation differs from already-existing
wml.variable.proxy in that it does not try to proxy table sub-fields,
and is fast & simple.

Example usage:
wml.variables.test = 123
print(wml.variables.test)
2018-01-19 09:53:06 +11:00
..
2018-01-19 09:53:06 +11:00
2017-11-11 13:50:35 +01:00
2017-06-21 20:45:21 -05:00