* Add checks when serializing
* Add default _estimateSize to generic inputs
* Fix multisig size estimation
* Change _addOutput to addOutput
* Add addInput and using that internally
* Split `getFee` out from `_updateChangeOutput`
100% code coverage for the preconditions module.
Usage:
```
$.checkState(something === anotherthing, 'Expected something to be
anotherthing');
$.checkArgument(something < 100, 'something', 'must be less than 100');
$.checkArgumentType(something, PrivateKey, 'something'); // The third
argument is a helper to mention the name of the argument
$.checkArgumentType(something, PrivateKey); // but it's optional (will
show up as "(unknown argument)")
```
Manuel Aráoz
Esteban Ordano