Implement the %?, %t, %e, and %; operators. Also implement the %<, %=,
%> operators, without which conditionals aren't very useful.
Fix the order of parameters for the arithmetic operators.
Implement the missing %^ operator.
Replace all potentially-failing operations with Err returns and add
tests.
Remove the Char parameter type; characters are represented as Numbers.
Fix integer constants to work properly when there are multiple constants
in the same capability string.
Tweak loop to use iterators instead of indexing into cap.
