Name section changes

[kripken]

Wasm is changing the Name section, WebAssembly/design#984, which we use when we emit code with -g. We should update our binary read/write code for that.

[lukewagner]

Politely requesting a ping whenever this change is ready to land so we can update browsers simultaneously. Because it's a custom section it's not a "breaking" change, but still it'd be nice to minimize the window of not-working-ness.

[tlively]

Not sure whether Luke ever got his ping, but he surely isn't still waiting on it. The name section has been stable for a long time now.