Implement List .sorted, .reversed, .at, et al

[Chuck]

These were discussed (and some even implemented) in a forum discussion or two. Don't have the links handy.

Depends on ticket:1 being completed.

May .at should be .get which could also be a dictionary method (offering a default arg when the key/index cannot be found).

[Chuck]

I'm part way through this.

[Chuck]

This is done for List. It might be interesting to also have a .toDictionary method, but this isn't required for 0.9 so I broke that out to ticket:150.