Move multi evaluation from API to an example

[keith-turner]

After #96 is complete, move Access.newEvaluator(Collection<Authorizations> authorizationSets) out the API to an example. The implemenation behind this API is really simple, the javadocs and impl for the API would be useful as an example.

[keith-turner]

Looked into making this change and found the current code is very well tested in addition to being well documented. Decided to leave it as is because its nice to have well tested and documented code to just use. Opened #100 to fix the docs.