gofmt on hopwatch.go.
Allows user to Enable or Disable hopwatch through code.

Instead of having to remove tons of hopewatch directive, one can now
`hopwatch.Disable()`, and `hopwatch.Enable()` in the code, in order to
skip a set of hopwatch commands that should not be active.
Merge pull request #4 from VonC/enable_or_disable

Enable or disable