Allow pretty printing of solutions
We currently generate very long lines with the solution of the problem (SAT, PB or MAXSAT).
We have OutOfMemory problems when displaying a solution after a OOM exception has ben launched.
It would probably not happen is the output stream is flushed regularly, i.e. after a limited amount of literals in the solution line.
It would therefore be nice to have a way to pretty print the solution line.
The only issue is that it may break scripts that simply do a grep to retrieve the solution.