docstring inheritance

Docstring inheritance, so that statements like:

```
In [1]: import clawpack.petclaw
In [2]: clawpack.petclaw.SharpClawSolver1D?
```

return 

```
Type:       type
String Form:<class 'clawpack.petclaw.sharpclaw.solver.SharpClawSolver1D'>
File:       /Users/aron/sandbox/clawpack/clawpack/petclaw/sharpclaw/solver.py
Docstring:
1D parallel SharpClaw solver.

Parent Class Documentation
==========================
 Two Dimensional SharpClawSolver

Parent Class Documentation
==========================

Superclass for all SharpClawND solvers.

Implements Runge-Kutta time stepping and the basic form of a
semi-discrete step (the dq() function).  If another method-of-lines
solver is implemented in the future, it should be based on this class,
which then ought to be renamed to something like "MOLSolver".

...
```