Create more optimized array types

[dibyendumajumdar]

Currently array types are an extension to Lua tables. This needs to be the case from a user perspective but from implementation point of view, arrays and slices could have a smaller data structure similar to userdata, rather than carrying the unused extra fields that come with the table type. So ideally we want to change the table type to be a union of standard Lua tables / and Ravi arrays. But this means that changes are necessary to GC etc. which is why so far I have not touched this.