Use pprint (aka script_repr) for __repr__

[ceball]

See #95:

We'd like __repr__ to be like the script_repr of this PR, but (a) Jim objects that using inspect is
overkill for __repr__ (but Jean-Luc and I don't see the problem) and (b) __repr__ shouldn't have the
indentation that script_repr has.

[jbednar]

It's just a gut feeling about avoiding self-aware code; if it really solves a real problem and makes it simpler to maintain and we don't care whether reprs are particularly fast to generate, then I don't have any objection. But yes, I think we should make a distinction between repr (all crammed onto one line, for various system purposes like debugging), and pprint (currently script_repr), formatted nicely for human beings.

[ceball]

Note: see #166 (comment)

[jlstevens]

Related to #100 and #396 these should be considered together.