Provide documentation for public API.

[YoEight]

Fixes #12

• [x] Document public API.
• [x] Add javadoc generation to GA. https://github.com/EventStore/TrainStation/pull/137

Breaking changes

• Reads and catchup-subscriptions from $all use StreamPosition internally now.
• NamedConsumerStrategy is no longer an enum.
• ESDB exceptions are all renamed and have the Exception suffix.

[YoEight]

Javadoc documentation is pushed on https://eventstore.github.io/EventStoreDB-Client-Java

[michael-schnell]

Any idea when this will be merged?

[YoEight]

PR is back to being mergeable again.