Support for labels

[gfwilliams]

They were left out because people generally don't use them now, but it looks like the Closure compiler sometimes uses them as a way to compact code.

[MaBecker]

Is this still relevant?

[gfwilliams]

I haven't seen them used in a long long time, but it's still part of the spec. I was kind of hoping they'd remove it in 'strict mode' or something like that, but it's still very much core spec.

[mfikes]

The ESP32 WROVERs (with the additional RAM) are a viable target for CloureScript on Espruino. ClojureScript uses Closure Compiler, so this label issue crops up in that scenario.