Add build.py
Add build.py

Create a build script modeled after hTools2's
(https://github.com/gferreira/hTools2_extension/blob/master/build-RF-extension.py)
as referenced by the RoboFont docs.

Unfortunately I can't get this to run because it obviously can't import
`mojo`. The `mojo` package doesn't seem to exist anywhere, or I can't
find it easily.

Instead I'm going to write a shell script to build the extension as it
seems like that will be easier.

teddywing/RoboFont-Equalize-Sidebearings-Key,teddywing/RoboFont-Equalize-Sidebearings-Key