Separate Show/Read for Name from the parser

[Blaisorblade]

Defining Read/Show to use concrete syntax for Name was coherent with using prettyprinting to implement Show for Term, but we stopped the latter, so we should at some point stop the former as well.

@Toxaris wrote that

the whole "use read as main constructor for names" business is broken

[Blaisorblade]

I'm on it. My plan is to have only derived instances of Show/Read, and not use them in the parser.

[Blaisorblade]

My plan is to have only derived instances of Show/Read, and not use them in the parser.

However, the existing code will be used (under another, non-overloaded name).