Move supporting javascript to abc interpreter repo
There was quite some duplicate code between this repository's interpret.js (used only to test the WebAssembly interpreter) and iTasks's abc-interpreter.js (used to run the interpreter and for JS interfacing). With this MR (and the corresponding iTasks-SDK!284 (merged)) all general code is moved to this repository and the JS interfacing code remains in iTasks. Hopefully most changes will now involve only one repository.
This MR also includes a change to the prelinked bytecode format: it now uses variable-length quantities to save roughly 70-75% on the final file size.