Riverbed replacement.
> git submodule update --init --recursive
# First - copy tools/build/emscripten-reference.txt -> tools/build/emscripten.txt
# and modify it so that it points at your emscripten install
# only needs to be done once
> build/tools/generate-projects.(sh/bat)
> cd build
# is the only command you need to run repeatedly
# it automatically reconfigures the needed files
> ninja