Add build with Docker, make and submodules

Starting to pull out hacks and custom instructions into a reproducible build.

Dockerfile

@@ -0,0 +1,5 @@
+FROM emscripten/emsdk:2.0.26
+RUN apt-get update && apt-get install -qqy autoconf autopoint libtool-bin pkg-config
+WORKDIR /src
+ENV EM_CACHE /src/deps/.emcache
+CMD ["sh", "-c", "emmake make -j`nproc`"]