Support different number syntaxes

```
These should work:

'oo' and '-oo' for infinity

'Inf', 'INF', 'NaN', etc

'2+3*I' or '2+4I' (SymPy and Mathematica style imaginary unit)

'2/3 + 4/5j' (rational parts for a complex number)
```

Original issue for #184: http://code.google.com/p/mpmath/issues/detail?id=144
Original author: https://code.google.com/u/111502149103757882156/
