Cloning Senders & Callers, Memory leak fix, return Aborthandle for intervals, various fixes & dependency updates

[jracollins]

Hi again @sunli829! 👋

Apologies for the large individual PR and list of changes - been meaning to create an upstream PR for a while for all of these features/fixes after using in production working off my fork.

This PR contains the following:

• Ability to Clone Senders & Callers using dynclone
  • Removes wrapping of CallerFn in a Mutex
• Adds Docs for Sender/Callers - Resolves Sender / Caller docu #44
• Small refactor in Broker to use remove Box<dyn Any + Send> and use Sender directly - asked in Sender / Caller docu #44
• Fixes infinitely growing slab for intervals (was causing OOM issues when using send_later repeatedly)
• Returns AbortHandle for intervals/send_later so that creator can cancel before completion if desired without stopping actor
• Changes ActorId to use usize rather than u64 - Resolves 32-bit platform error #41
• Bumps dependencies to latest versions
• Added Eq to compare Callers/Senders

[sunli829]

@jracollins Thanks!