BUG: p2c not reliable in scatter or gl2d

[destradafilm]

Based of this example by @etpinard
http://codepen.io/etpinard/pen/EyydEj

If you zoom or pan, the p2c conversion is unreliable

[etpinard]

That p2c and other x2y conversion functions aren't official features by any means and aren't guaranteed to work. That codepen I wrote is grade-A hack.

What I think we should do: is add another plotly_ event (e.g. plotly_mouse) that would get fired on anytime you mouse over a graph with or without triggering plotly_hover.

[destradafilm]

I vote for that ploty_mouse event

[etpinard]

@destradafilm great. I'll close this issue then and merge it with #145

[therealsquidgee]

Hey @destradafilm not sure if you still need this but I slightly modified @etpinard 's codepen to make the mousemove event more reliable (still a grade A hack though and it will error if the start and end of the x range are equidistant from 0 e.g. [-12, 12] or something like that).

http://codepen.io/therealsquidgee/pen/EmbOzX