Refactoring `Bonds` class with the following changes...
Refactoring `Bonds` class with the following changes...

* Adding a `fmtstr` attribute and corresponding property
  getter/setter methods
* Removing custom `__str__` method
* Adding a `todict` method.
* Other minor hacks.

androomerrill/scikit-nano,androomerrill/scikit-nano,scikit-nano/scikit-nano,scikit-nano/scikit-nano