This updates the dependency manager to use go modules instead of dep so
that we can remove dep as a dependency and we can begin using and giving
feedback on modules within this project. It should simplify dependency
management and make it faster to run the builds too.
The big change is updating the various Makefiles to stop relying on the
vendor directory because it no longer exists. This change creates a
`tools.go` file with the revisions of the tools we use that are currently
in the `required` section of `Gopkg.toml`. We are currently in other
discussions to modify how we handle tool dependency management, but this
change does not change that.
Jonathan A. Sternberg