Cannot build on windows

[mandarl]

Get the below error when I try to go build on windows:

$ go build
# github.com/zach-klippenstein/goadb
.\server.go:140: undefined: unix.Access
.\server.go:140: undefined: unix.X_OK

The unix package is not available on windows. Need conditional compilation. I don't see any reason this library cannot be supported on windows.

[mandarl]

I have created pull #23 with the conditional build files