Clear search when :search without args is given.

Needed for #564 because :search "" won't work anymore.

doc/help/commands.asciidoc

@@ -35,7 +35,7 @@
 |<<report,report>>|Report a bug in qutebrowser.
 |<<restart,restart>>|Restart qutebrowser while keeping existing tabs open.
 |<<save,save>>|Save configs and state.
-|<<search,search>>|Search for a text on the current page.
+|<<search,search>>|Search for a text on the current page. With no text, clear results.
 |<<session-delete,session-delete>>|Delete a session.
 |<<session-load,session-load>>|Load a session.
 |<<session-save,session-save>>|Save a session.
@@ -394,9 +394,9 @@ Save configs and state.
 
 [[search]]
 === search
-Syntax: +:search [*--reverse*] 'text'+
+Syntax: +:search [*--reverse*] ['text']+
 
-Search for a text on the current page.
+Search for a text on the current page. With no text, clear results.
 
 ==== positional arguments
 * +'text'+: The text to search for.

qutebrowser/commands/runners.py

@@ -79,8 +79,8 @@ class SearchRunner(QObject):
 
     @pyqtSlot(str)
     @cmdutils.register(instance='search-runner', scope='window', maxsplit=0)
-    def search(self, text, reverse=False):
-        """Search for a text on the current page.
+    def search(self, text="", reverse=False):
+        """Search for a text on the current page. With no text, clear results.
 
         Args:
             text: The text to search for.

qutebrowser/config/configdata.py

@@ -1189,4 +1189,5 @@ CHANGED_KEY_COMMNADS = {
     'open -w about:blank': 'open -w',
     'download-page': 'download',
     'cancel-download': 'download-cancel',
+    'search ""': 'search',
 }