Add a :tab-detach command.

See #62.

doc/help/commands.asciidoc

@@ -45,6 +45,7 @@
 |<<stop,stop>>|Stop loading in the current/[count]th tab.
 |<<tab-clone,tab-clone>>|Duplicate the current tab.
 |<<tab-close,tab-close>>|Close the current/[count]th tab.
+|<<tab-detach,tab-detach>>|Detach the current tab to its own window.
 |<<tab-focus,tab-focus>>|Select the tab given as argument/[count].
 |<<tab-move,tab-move>>|Move the current tab.
 |<<tab-next,tab-next>>|Switch to the next tab, or switch [count] tabs forward.
@@ -508,6 +509,10 @@ Close the current/[count]th tab.
 ==== count
 The tab index to close
 
+[[tab-detach]]
+=== tab-detach
+Detach the current tab to its own window.
+
 [[tab-focus]]
 === tab-focus
 Syntax: +:tab-focus ['index']+

qutebrowser/browser/commands.py

@@ -109,7 +109,7 @@ class CommandDispatcher:
             raise cmdexc.CommandError("No WebView available yet!")
         return widget
 
-    def _open(self, url, tab, background, window):
+    def _open(self, url, tab=False, background=False, window=False):
         """Helper function to open a page.
 
         Args:
@@ -404,6 +404,15 @@ class CommandDispatcher:
         qtutils.deserialize(history, newtab.history())
         return newtab
 
+    @cmdutils.register(instance='command-dispatcher', scope='window')
+    def tab_detach(self):
+        """Detach the current tab to its own window."""
+        url = self._current_url()
+        self._open(url, window=True)
+        tabbed_browser = self._tabbed_browser()
+        cur_widget = self._current_widget()
+        tabbed_browser.close_tab(cur_widget)
+
     def _back_forward(self, tab, bg, window, count, forward):
         """Helper function for :back/:forward."""
         if (not forward and not