Make uTransformers faster

Using the emscripten-fastcomp [1] backend is best practice for emscripten, and significantly improves performance.

This, unfortunately, complicates the build process, especially if we are building [1] from source. However, there are a number of potential solutions that will be investigated in #15.

### References

[1] https://github.com/kripken/emscripten/wiki/LLVM-Backend