To build the demo...
1. Install harfbuzz into 'third_party/externals/harfbuzz'
e.g. > mkdir third_party
> cd third_party
> mkdir externals
> cd externals
> git clone git@github.com:harfbuzz/harfbuzz.git
This only needs to be done once, but it is not checked in as part of
this repo, so it must be done if you want to rebuild from sources.
2. > make
This should build everything, and copy the necessary files into docs/
You need to have the embind tools installed for this to build.