Feature request: restore default font (setfont)

[Tecol87]

On a lot of distributions, the default font (e.g. ter-u32b) is not available as file since terminus-font is not installed. The default font can be restored with this code. This can be important, when the current font is garbage (https://github.com/legionus/kbd/issues/94) or not as readable as the default font.