Newt should use Go modules

[d3zd3z]

Now that Go has official module support (and by September, GOPATH will be deprecated), Newt should be made so that it can build using modules. This would eliminate the need for build.sh as with modules, it would be possible to just cd to newt and type go build.

I few things that seem to need changes:

• Create go.mod files in the appropriate places.
• Fix spelling of Sirupsen -> sirupsen in any import statements. With modules, this will have to match the github user's name.
• Fixing up any necessary dependencies.
• Redoing the vendoring. Go modules support vendoring, although it is much less necessary, it can still be done.