To bring it inline with the improved and mandatory `go.mod` package system

[wade-welles]

I removed the use of Gopkg module management and replaced it with go.mod that is much improved now, and mandatory in modern versions of Go (which I'm not actually a fan of but besides the point).

I was unable to build it before but now you can easily build it by pulling it down, calling go mod tidy and go mod build

I also updated the Makefile too, so now someone wanting to build it from source should now be able to simply clone it and run the make and it will build.