chore(cmd): move cmd into fleetctl

this make go install behave correctly.
feat(*): use goven instead of third_party.go
feat(build): introduce a build-release script

This will cross compile fleet for OSX and Linux. Windows needs love for
the terminal stuff.
Merge pull request #101 from philips/add-build-release-script

Add build release script
Merge pull request #98 from robszumski/master

feat(docs): document x-conflicts
fix(contrib): Rename corectl-inject-ssh.sh to fleetctl-inject-ssh.sh