Include stdio.h directry in debug.h
Clean obsolete debug prints
Add option to seek up to selected filetree depth

Expand only -d (--tree-depth) directory levels from the argument
directories. If 0, no directories will be expanded. The default is to
expand indefinately.
Add man page
Fix digest_cmp()

Don't use strcmp(), the needed cast from unsigned char * to char *
messes the comparison up. Use custom comparison instead.
Remove possible trailing slashes from input files