Use GOPATH relative import paths

When using 

    go get github.com/mirmorphic/hwio

 I am unable to get the examples to compile because the import paths assume hwio is relative to GOPATH/src. It would be really helpful if we could follow the go convention of using the public go repo paths, because then I can run the examples using go run. e.g.

    go run examples/pinmap.go

I checked Dave Cheney's gpio project and his examples seem to use this convention. I've tested this change on a live BBB using Arch Linux. Many Thanks.