disruptor-rs

Minor documentation improvements:

• Improve intro to crate in the README.
• Move sections around.

• Add a poll_take(u64) method to the EventPoller API to limit the number of events returned.
• Thanks to https://github.com/kradskymer for suggesting the feature.

• Also make producer barriers part of the public API so their types can be named in e.g. fields in a struct (if you want to store e.g. an EventPoller).

• Improvements to documentation.
• Make consumer barriers visible in docs so they're importable in client code.

• Add Event Poller API where clients can control their own thread(s) and poll for new events in a non-blocking way.
• The Event Poller API supports batch processing via the Iterator and ExactSizeIterator traits.
• Performance is the same as when the Disruptor controls processing thread(s). See the benchmark poller.