Implement DynamicReset on standard library containers?

[estokes]

Right now it is not possible to use standard container types like HashMap directly in a dynamic pool, and that is too bad because it would be very convenient. The reason is that DynamicReset is defined in the dynamic-pool crate, and HashMap is defined in the standard library, so users of this crate are not allowed to implement DynamicReset for HashMap. However dynamic-pool could provide those implementations because you define the trait.