Give names to some phrases

[lukacslacko]

We could introduce a NAMED_PHRASES in the phrase.rs thread_local, and map some Phrases to a string. A typical example would be to map S(0) to "1". Then, it should have something like short_string which should look itself up in that, and if it finds itself, it should return that name instead of the expansion, and it should recursively call short_string on the subphrases, and FAX should use short_string by default, and something else could do the full print.