Set font style with the following attributes:
        'foreground_color', 'background_color', 'italic',
        'bold' and 'underline'

def set_style(self):
        """
        Set font style with the following attributes:
        'foreground_color', 'background_color', 'italic',
        'bold' and 'underline'
        """
        if self.current_format is None:
            assert self.base_format is not None
            self.current_format = QTextCharFormat(self.base_format)
        # Foreground color
        if self.foreground_color is None:
            qcolor = self.base_format.foreground()
        else:
            cstr = self.ANSI_COLORS[self.foreground_color-30][self.intensity]
            qcolor = QColor(cstr)
        self.current_format.setForeground(qcolor)
        # Background color
        if self.background_color is None:
            qcolor = self.base_format.background()
        else:
            cstr = self.ANSI_COLORS[self.background_color-40][self.intensity]
            qcolor = QColor(cstr)
        self.current_format.setBackground(qcolor)

        font = self.current_format.font()
        # Italic
        if self.italic is None:
            italic = self.base_format.fontItalic()
        else:
            italic = self.italic
        font.setItalic(italic)
        # Bold
        if self.bold is None:
            bold = self.base_format.font().bold()
        else:
            bold = self.bold
        font.setBold(bold)
        # Underline
        if self.underline is None:
            underline = self.base_format.font().underline()
        else:
            underline = self.underline
        font.setUnderline(underline)
        self.current_format.setFont(font)