Documentation! (Finally...)

New features:
- interpolation (check out the new example)
- initial hiding of series
- right click on legend to show just one series
- the various hiding and fading stuff are exposed in JavaScript (but this isn't documented... yet?)

Other changes and fixes:
- proper handling of "not using a data series"
- refactoring some event handlers
- reading from external data source works properly now (for the same domain)... turns out that the mock was still there
- inheritance of use_markers fixed
- tooltips now have borders and backgrounds and are sized