Add makefile for building

This add's a makefile that automates:
- Getting/Installing go
- Setting up paths
- Installing dependencies, godep, etc.
- Building the binary

Review: @jrconlin r?
for this, since we're running through godep, probably should change ```$(GOCMD) to ```$(GODEPCMD) go```

Since 'go' is a command, we don't need to specify a path.