* Split out notifying /sync requests and calculating sync responses

The logic for notifying /sync requests is about to get really
complicated as we optimise when to wake up requests, so split
out that code into a separate struct to isolate it and make
it easier to unit test.

Improve logging configuration

Add Apache Version 2.0 license and headers to all golang files

Improve naming consistency

When LOG_DIR or so is not specified, just configure the formatter.

This has the following known shortcomings:
 - It doesn't handle missing events not in the from/to range.
 - It doesn't order events in the timeline correctly.
 - It doesn't handle invited/left rooms at all.
 - There is no intelligent wakeup logic: events for Bob will wake up Alice's stream.

Also ensure every sync response has a `next_batch` token by forcing
it in the constructor, as previously timeouts would not have a token.