Simplify API for data collectors.
DRY up some serialization.
More DRYing.
Out xml attributes in alphabetical order.

Note - this doesn't fully work, since JAXB insist on adding properties from a superclass last.
Code formatting.
TimingDataCollector can't be abstract, it's being used when running Firefox.
Rename, and expand use of, checks if various timing apis are supported by the current browser.
Include version of Browsertime in page info.
Don't drop accuracy of firstPaint time by converting double to long.
Code formatting.
Specify user timing marks as relative (to navigation start), instead of as absolutes time stamps.
Support for reading resource timing.