Improve pretty-printing /parsing of types using UTF-8 Symbols
It would be nice if CDuce was able to pretty-print types with UTF-8 connectives. This would depend on #34. Some requirements :
- It needs to be automatically disabled for terminals that don't support UTF-8
- A user must be able to disable it with a command-line flag
- This should also work for parsing. A rule of thumb to ensure the correct pretty-printing of types is that CDuce should always be able to parse a type it has pretty-printed (such that both types are equivalent).