examples of usage with the important unu commands

enable the unu 2op and 3op operations that output integers to save
the output as, say, signed char, instead of float.  This is different
than being able to change input type, for operations like "gt".

make darn sure that nobody uses printf(), only fprintf()

standardize and document use of special single characters
for meaning as unrrdu arguments:
M : max position along an axis, equal to #samples-1
# : ?
- : standard in and standard out
any others?
