Unbind events

[maplemuse]

This addresses #38 by ensuring that events are properly unbound on shutdown.

I updated the many-series example page to better show the before/after results.
Load the page, perform a heap snapshot in Chrome. Click the replot link, then perform a second heap snapshot.
Finally, click again, perform a third heap snapshot. Select the third snapshot, and select items created between snapshots 1 and 2.
Before the second commit, you will see that the plot tooltip plot hover event handlers remain, leaking memory.

[maplemuse]

I've done further changes as well which get much more drastic. I changed from the prototype.init code that was there previously to the shorter, simpler nested functions. I didn't add this to the pull request yet, as it's a much more drastic change.

[krzysu]

just remember that the tooltip needs to support multiple instances :)

[maplemuse]

My primary environment is a web dashboard with six plots, updating with new data frequently.