Option for output of factor(n) as string

At times, it is desirable to incorporate the default REPL output of factor(n) into strings for use, for example, within a println command. It would be nice to have a type variant - factor(String,n) - which outputs in string form (eg/ factor(String,90) = "2 * 3^2 * 5"), as well as a method for converting a Factorization form into a nice string (eg/ prodform(factor(90)) = "2 * 3^2 * 5").

Start by locating the factor(n) entry point and the Factorization display or formatting code. Compare the requested factor(String,n) and prodform(factor(n)) examples, then add coverage showing that both produce the expected string form for 90 and related factorizations.

Written by the indexing model from the issue text.