Move to go modules for dependency management

[shanson7]

In the next release of golang (1.17) support GOPATH builds is going to be removed. Migrating to modules seems the way to go to future proof this project.

[Dieterbe]

i've tried it once or twice and both times it became painful and i gave up, but i also wasn't super motivated.
FWIW i didn't see a clear deprecation notice on https://golang.org/doc/go1.17 and at least this seems to work fine still:

GO111MODULE=off make

[Dieterbe]

#1999

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[shanson7]

I think this will need to be done eventually.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.