Update: Revert back to 'char' rather than 'unsigned char'.

Update: Revert back to 'char' rather than 'unsigned char'.

There are a lot more changes that I realized.
changing 'char' to 'unsigned char' will be for the next development release after the upcoming stable release.

Introduce the f_char_t type to allow for easier switching from 'char' to 'unsigned char'.

In all places that us 'unsigned char', just switch to 'char'.

Move the directory '..' and '.' into static strings.