added center windowrule

src/config/ConfigManager.cpp

@@ -571,6 +571,7 @@ void CConfigManager::handleWindowRule(const std::string& command, const std::str
         && RULE.find("monitor") != 0
         && RULE != "nofocus"
         && RULE != "noblur"
+        && RULE != "center"
         && RULE != "fullscreen"
         && RULE.find("animation") != 0
         && RULE.find("rounding") != 0

src/events/Windows.cpp

@@ -224,6 +224,8 @@ void Events::listener_mapWindow(void* owner, void* data) {
                 } catch (...) {
                     Debug::log(LOG, "Rule move failed, rule: %s -> %s", r.szRule.c_str(), r.szValue.c_str());
                 }
+            } else if (r.szRule == "center") {
+                PWINDOW->m_vRealPosition = PMONITOR->vecPosition + PMONITOR->vecSize / 2.f - PWINDOW->m_vRealSize.goalv() / 2.f;
             }
         }