Add test suite for API completeness.

I noticed that crypto-browserify is missing the `pseudoRandomBytes` from the node crypto API.   There is a comment in the code that suggests you want to at least provide a stub function: 
```javascript
// the least I can do is make error messages for the rest of the node.js/crypto api.
```
I looked around but couldn't find a reason not to provide `pseudoRandomBytes`.   In addition, there are several other functions missing as demonstrated by this test code.  Is there interest in keeping the interface fully consistent?