Example implementations for hashCode() in documentation

[offbynull]

What happened

While documentation does exist that explains hashCode(), that documentation is lacking and doesn't provide many (any?) implementation examples. It would nice for users to...

1. see a hashCode() implementation example.
2. be provided with a quick list of best practices.
3. be provided with a quick overview of how hash() works.

The implementation example could be as simple as just calling into hash() several times and mixing the results:

return Immutable.hash(this.numeric_field) ^ Immutable.hash(this.string_field) ^ Immutable.hash(this.boolean_field));

How to reproduce

Go ask a person unfamiliar with hashCode()/equals() to read the documentation and attempt an implementation for some custom object.