Fix improper julia specification
Specify function argument types in `Base.map` implementations

The type wasn't specific enough and was being dispatched to a generic implementation in Base.
Use try/catch in tests instead of `=> :throws`
Style-related refactoring
`assoc` instead of `update` in benchmarks
More TODOs
`contains` deprecated in favor of `in`
Remove unused `DenseNode` constructor
Adds a `@Persistent` constructor macro
Allows constructing persistent sets with `@Persistent`
Favor `@Persistent` macro constructor in README