Rename from immutable to persistent

There is some immediate backlash about immutable collections by Java users, as their understanding of the concept is either getting a full copy per operation, or receiving an exception on mutating methods.

The persistent keyword along with some references to Big O perf in the documentation may help spread the understanding of the difference.

[GlenKPeterson]

In the Java world, “Persistent” has always meant “stored in a database”. It’s the “P” in “JPA”, which is why I steered away from it. Either way, whatever words you use for immutable/persistent collections should be less typing than the name for Mutable ones (and Unmodifiable ones) in order to steer lazy programmers toward doing the safest thing.

[cbruegg]

I like this idea, but it looks like implementations of the ImmutableCollection interface don’t have to be persistent. That being said, perhaps the concrete implementations should contain the word Persistent.