Added a build script

Added a build script, named *Build.fsx*, together with *build-release.sh* and *build-release.cmd* batch files.

FAKE 3.2.1 and xunit.runners 1.9.2 have been included in source control and make the diff output big, otherwise there are only 3 files to look at:
* Build.fsx
* build-release.sh
* build-release.cmd

This Pull Request is related to #9.