cleanup: rename package and vendor dependencies for old go versions

Fixes #8 and begins to address deployability.

vendor/github.com/pebbe/zmq4/socketget_windows.go

@@ -0,0 +1,26 @@
+// +build windows
+
+package zmq4
+
+/*
+#include <zmq.h>
+*/
+import "C"
+
+import (
+	"unsafe"
+)
+
+/*
+ZMQ_FD: Retrieve file descriptor associated with the socket
+
+See: http://api.zeromq.org/4-1:zmq-getsockopt#toc9
+*/
+func (soc *Socket) GetFd() (uintptr, error) {
+	value := C.SOCKET(0)
+	size := C.size_t(unsafe.Sizeof(value))
+	if i, err := C.zmq_getsockopt(soc.soc, C.ZMQ_FD, unsafe.Pointer(&value), &size); i != 0 {
+		return uintptr(0), errget(err)
+	}
+	return uintptr(value), nil
+}