boi'ai VUhU experimental cmavo

unary mekso operator: immediately convert number into a single digit.

See: http://mw.lojban.org/papri/Proposal:_distinguishing_digits_from_numbers#Clean-Up


In notes:

ku'oi'u
closing bracket/terminator for mekso expression interpretation modifiers
mu'i'u (exp!)
base-dependent digit: representing exactly one half of one more than the maximum possible single-digit number expressible in the relevant number base
vu'ai (exp!)
base-dependent digit: the maximum possible single-digit number expressible in the relevant number base.