Added a basic Go webhook handler

I'm pushing this out because the Docker build actually requires getting the Go
application from GitHub when building the image.  Perhaps I should find a way
to get it to use only the local version to avoid lots of extra commits.  But I'm
just testing the build process (not the application) so I think just getting it
bootstrapped should be sufficient.

Author: mtiller

docker/Dockerfile

@@ -63,3 +63,5 @@ USER builder
 WORKDIR /opt/MBE
 
 RUN git clone https://github.com/xogeny/ModelicaBook.git
+
+RUN go install xogeny/pubbook