Un-indents text at cursor position.

def unindent(self):
        """
        Un-indents text at cursor position.
        """

        _logger().debug('unindent')
        cursor = self.editor.textCursor()
        _logger().debug('cursor has selection %r', cursor.hasSelection())
        if cursor.hasSelection():
            cursor.beginEditBlock()
            self.unindent_selection(cursor)
            cursor.endEditBlock()
            self.editor.setTextCursor(cursor)
        else:
            tab_len = self.editor.tab_length
            indentation = cursor.positionInBlock()
            indentation -= self.min_column
            if indentation == 0:
                return
            max_spaces = indentation % tab_len
            if max_spaces == 0:
                max_spaces = tab_len
            spaces = self.count_deletable_spaces(cursor, max_spaces)
            _logger().info('deleting %d space before cursor' % spaces)
            cursor.beginEditBlock()
            for _ in range(spaces):
                cursor.deletePreviousChar()
            cursor.endEditBlock()
            self.editor.setTextCursor(cursor)
            _logger().debug(cursor.block().text())