Add ability to pass -image parameter, fixes for new AST

[mbullington]

Hello! I'm using js-wasmc and it's great, however I wanted to be able to use it with the latest EMSDK version. Few tweaks to allow that without changing js-wasmc functionality:

• Allow for specifying an -image parameter in the build step.
  • I used this to point to mbullington/emsdk, which is a downstream version of emscripten/emsdk I just added Ninja to and removed Java.
• Fixes in the package step for the new Module[...] syntax for mangled names.
• Fix Node.js trying to load .wasm file on new version of EMSDK.

Thanks!

[mbullington]

I think -docker-image sounds good. Will work on that shortly.

[mbullington]

Hi @rsms, pretty sure my latest commits meet your requested changes. I'm using this over at https://github.com/mbullington/astro-wasm and the changes work well.

Best