Implement reactivePoll and reactiveFileReader
Implement click and hover events on static plots

plotOutput now takes clickId and hoverId params that tell Shiny
where to send click and hover events for that plot. The server.R
file can listen on input$<clickId> and/or input$<hoverId>. In
both cases, the resulting value will have numeric x and y elements
that indicate the mouse position in user coordinates. In the case
of hover events, it's also possible to have a NULL value which
means the mouse is not currently hovering over the plot.
Retina display compatibility
Fix Retina compatibility (revert b113119)
Make hover delay configurable
Merge pull request #191 from trestletech/master

Restrict the number of observations to a valid, positive number.
Merge pull request #182 from jcheng5/reactive-poll

Implement reactivePoll and reactiveFileReader
Use crosshair cursor when plot supports hover/click
Merge pull request #183 from jcheng5/plot-mouse-events

Click and hover on static plots. Also, fix retina compatibility and make hover delay configurable
Add session$onFlush and session$onFlushed
Merge pull request #192 from jcheng5/flush-callbacks

Add session$onFlush and session$onFlushed
Firefox locator compat
Fix locator Retina compatibility. Again.

Was working locally on Macs but not on spark.rstudio.com accessed via rMBP.
Simpler math
Configurable hover delay type (debounce/throttle)