Improve async and custom type support

[timstableford]

• Added support for catch and finally
• Cope better with top-level coroutine.yield() calls
• Made doString and doFile async
• Added support for type extensions This framework allows plugging in types that should be converted to user data and have a metatable with methods. JS classes fit particularly well into this. This replaces JS references.
• Converted Promise to type extension and made the functions on it into proper methods. Also added Promise.create and Promise.all.
• Added Error as a type extension.
• Allow returning arrays from Lua

[ceifa]

I loved the type extension idea! But maybe it is very tied to metatables, no? Would be nice to pass some other types to it, like function, thread, etc.

[timstableford]

An extension doesn't necessarily need a metatable as long as it implements push value and get value. My thought was to leave these default handlers in here but there's no reason at all that they couldn't all be removed to an extension if you'd like?

[ceifa]

An extension doesn't necessarily need a metatable as long as it implements push value and get value. My thought was to leave these default handlers in here but there's no reason at all that they couldn't all be removed to an extension if you'd like?

Nice, so it's okay. we can leave it that way and maybe migrate some other types later

[timstableford]

An extension doesn't necessarily need a metatable as long as it implements push value and get value. My thought was to leave these default handlers in here but there's no reason at all that they couldn't all be removed to an extension if you'd like?

Nice, so it's okay. we can leave it that way and maybe migrate some other types later

I was incorrect, it required a small tweak. It already was fine for pushValue but getValue meant adding a new isType handler