Misc: stoppaint_force & Documentation update

- Add stoppaint_force option, controlled via D-Bus, to stop painting
  completely, which may look better than unredirecting the screen,
  sometimes. (#41)

- Add x2, y2 matching targets.

- Update documentation.

src/common.h

@@ -462,6 +462,8 @@ typedef struct {
   bool unredir_if_possible;
   /// Forced redirection setting through D-Bus.
   switch_t redirected_force;
+  /// Whether to stop painting. Controlled through D-Bus.
+  switch_t stoppaint_force;
   /// Whether to enable D-Bus support.
   bool dbus;
   /// Path to log file.