Modifies the behavior of the interpreter on crash under Emscripten:
1. No Python traceback shown on segfault/trap
2. The JavaScript source line is shown
The JavaScript source line is super long and completely unenlightening,
whereas the Python traceback is very helpful.
Moves the Emscripten web example into a standalone folder, and updates
Makefile targets to build the web example. Instructions for usage have
also been added.
This unifies the code for nodejs and the code for the browser. After this
commit, the browser example doesn't work; this will be fixed in a
subsequent update.
Add emscripten.py script to automate emscripten build.
This is modeled heavily on `Tools/wasm/wasi.py`. This will form the basis of an Emscripten build bot.
