At this stage printf is very young and limited, as it hopefully
will be developed along with BDSH. Functionality is heavily related
on libc printf already available. BDSH printf implements only 3 format
flags, with no options/precision/width modifiers allowed. Also,
one output control is available - '\n'. '\' character stands
as an escape character, i.e. every special character after it
will be treated as general char and will be printed out.
What's missing:
 * Error checking for format string.
 * Add more output controls (\t \r ...)
 * Add width/precision options for number printings
 * Add more format flags (%f %b ...)