Set up CI build for building gh against different platforms

[owenthereal]

Building gh requires cgo. It's due to a limitation of cross compilation on accessing system root certificates.

The current approach is to use a cross compilation tool to build for the current platforms for i386 and amd64, but it's built on a native platform through virtual box. I'm using this gotask to make a build.

It'd be nice to have ec2 do the job. Also travis-ci seems to support OSX VMs but I never try it.

Relative discussion: #138 (comment)

[calavera]

Unfortunately I don't think Travis lets build have a build matrix with different distros/OS. I cannot find anything in their help, it looks like they discriminate by language, and I say Konstantin commenting this on twitter:

https://twitter.com/konstantinhaase/status/414861045212381184

[owenthereal]

I just read that. Ya...it's hard to find a service that has different distros/OS to build Go stuff. I think people set up plain EC2 servers themselves.