Type discrepancies

I've had to change some types a little. First of all, the original release of dvilj declared bool as char. OSlib, however, uses unsigned int which is longer so to avoid certain chaos I had to adapt bool to an int-sized datum.
Another change was made with OSlib's file descriptor type, os_f. This is originally unsigned char but was changed to int, the reason being dvilj requires a bigger filetype because it uses special conventions for file descriptors stored in a font descriptor struct:

• NULL means there hasn't been an attempt made to open the font yet.
• -1 means the font file doesn't exist.
• All other values are interpreted as legal file descriptors.

This is OK since with APCS all non-floating point arguments are passed as word-sized data. The only occasion where problems could occur is when you're passing an os_f * because in that case the top 3 bytes are undefined. That's why I'm initializing the file descriptor with 0 when I have to do this.