Add 'const' to PROGMEM font declarations
Use of unsigned char instead of char

In order to display non ascii chars, we need to be able to go outside the range of -128/127 the char type handles.

Using `unsigned char` let us handle extend ascii chars till 255.
Update DMD.h
Removing unecessary cast
Added a font with non ascii chars
Added a font with non ascii chars
Removed font with wrong name
Merge branch 'patch-1' of github.com:xseignard/DMD into patch-1
Better explenation of the added font

- Renamed it to an explicit name
- Added comment on the font mentionning the charset.