Go Module Support

This release packages each transport as an individual Go module.

In order to accomplish this, the transport packages had to adopt the Go semantic import convention. Therefore, the import paths have changed. For instance, the obfs4 transport package was previously called "github.com/OperatorFoundation/shapeshifter-transports/transports/obfs4" and it is now called according to Go convention "github.com/OperatorFoundation/shapeshifter-transports/transports/obfs4/v2".