printf, but recoded

It handles the following range of conversion specifiers:

• %c (single character)
• %s (string)
• %d and %i (signed decimal integer)
• %u (unsigned decimal integer)
• %p (void *pointer argument converted to hexadecimal)
• %x (unsigned hexadecimal integer, in lowercase)
• %X (unsigned hexadecimal integer, in uppercase)
• %% (for writing a single % character)