Refactor process.go for platform specific

Signed-off-by: John Howard <jhoward@microsoft.com>

runtime/process_windows.go

@@ -0,0 +1,19 @@
+package runtime
+
+import "os"
+
+// TODO Windows: Linux uses syscalls which don't map to Windows. Needs alternate mechanism
+func getExitPipe(path string) (*os.File, error) {
+	return nil, nil
+}
+
+// TODO Windows: Linux uses syscalls which don't map to Windows. Needs alternate mechanism
+func getControlPipe(path string) (*os.File, error) {
+	return nil, nil
+}
+
+// TODO Windows. Windows does not support signals. Need alternate mechanism
+// Signal sends the provided signal to the process
+func (p *process) Signal(s os.Signal) error {
+	return nil
+}