Add HTML-entity to text processor

 - Allows using '<' '>' characters that would otherwise be
   interpreted as tag characters
 - Allows using '&' that would now otherwise be
   interpreted as entity
 - Extensible

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Add "&#xxxx;" and "&#hxxxx;" unicode char entites

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
[fix] Only set new canvas size if it actually can resize

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Add sgui_window_pack function

Function computes the bounding box of all widgets and resizes the window
to fit closely to the box. The borders to the left and top are added to
the right and bottom.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>