Add shortcut to move a line up and down

Pressing Alt+Arrow Up / Alt+Arrow Down will move the current line
up/down. This is a nice feature to move lines without having to do a
Select-Cut-Move-Paste manipulation.

ReText/editor.py

@@ -246,6 +246,36 @@ def keyPressEvent(self, event):
 					# Insert Markdown-style line break
 					cursor.insertText('  ')
 				self.handleReturn(cursor)
+		elif key == Qt.Key_Down and event.modifiers() & Qt.AltModifier:
+			# Select the current block
+			cursor.movePosition(QTextCursor.StartOfBlock, QTextCursor.MoveAnchor)
+			cursor.movePosition(QTextCursor.NextBlock, QTextCursor.KeepAnchor)
+			text = cursor.selectedText()
+			# Remove it
+			cursor.removeSelectedText()
+			# Move to the next block
+			cursor.movePosition(QTextCursor.NextBlock, QTextCursor.MoveAnchor)
+			# Paste the previous line
+			cursor.insertText(text)
+			# Move to the pasted block
+			cursor.movePosition(QTextCursor.PreviousBlock, QTextCursor.MoveAnchor)
+			# Update cursor
+			self.setTextCursor(cursor)
+		elif key == Qt.Key_Up and event.modifiers() & Qt.AltModifier:
+			# Select the current block
+			cursor.movePosition(QTextCursor.StartOfBlock, QTextCursor.MoveAnchor)
+			cursor.movePosition(QTextCursor.NextBlock, QTextCursor.KeepAnchor)
+			text = cursor.selectedText()
+			# Remove it
+			cursor.removeSelectedText()
+			# Move to the previous block
+			cursor.movePosition(QTextCursor.PreviousBlock, QTextCursor.MoveAnchor)
+			# Paste the previous line
+			cursor.insertText(text)
+			# Move to the pasted block
+			cursor.movePosition(QTextCursor.PreviousBlock, QTextCursor.MoveAnchor)
+			# Update cursor	
+			self.setTextCursor(cursor)
 		else:
 			if event.text() and self.tableModeEnabled:
 				cursor.beginEditBlock()