yabm uses it's own bitmap font format, each character is stored in a 8x8 matrix.
One unsigned byte represents one row and each bit represents a pixel on that row. 

The makefont.c program takes an 8x8 sized PNG image as input and outputs
the font data as 8 unsigned byte in hex.
This output has to be compiled into ha header-file which in turn 
can be used be mypng_printf()