This resolves #18, but without catching zero, which is a valid key.

Added a legend 'reverse' sorting option.

This orders the legend entries in reverse order of their series.

Added the plot function as a chainable property.

Modern browser consoles obviate the need for an object logging function.

The previous processing step already guarantees that the values are
numeric.

This resolves #534 by handling the case where data is a string, whether
it is provided alone or as a pair.  We can also eliminate the old and
unnecessary check for undefined values.

Resolves #734 and #816.

Fix inability to set the point lineWidth to 0.

This resolves #895.

This temporary fix addresses the problem described in #810, and possibly
#945, where calls to setData for a pie chart do nothing.

The canvasWidth, canvasHeight, legendWidth and legendHeight variables
existed only to share data between the setupPie and draw functions.  Now
that setupPie has been folded into draw, they're no longer necessary.

This code is only used to prepare the plot for drawing; inlining it is
cleaner and will allow us to get rid of some plugin-global variables
that existed only to give setupPie a way to share data with the draw
function.

The redraw flag starts out as true, then is immediately set to false on
draw.  If labels are enabled, drawPie calls drawLabels, which calls
drawLabel for each label.  Any label that can't fit sets redraw back to
true, so the whole process can repeat.

This isn't the most obvious mechanism, and forces one to remember to do
things like setting redraw back to true after drawing, so the plot can
redraw itself on resize or when setting new data.

Instead we now have drawPie return true when it drew successfully, and
false otherwise, which the same happening in drawLabels and drawLabel.
Instead of checking the flag, we now just check the return value.

This has the added benefit of slightly improving performance in the case
where several redraws are necessary, since it now short-circuits out of
the draw loop as soon as one label fails to fit.

The total is only used within the combine function; it doesn't need to
exist at the top level of the plugin.

They're small and not used anywhere else, so keeping them in separate
functions only serves to increase complexity.

In plugins we should never add hooks conditionally; the condition should
remain within individual hooks, so the plugin can be toggled at any
time.

Ideally we should also 'inline' the hook functions, since they're used
nowhere else.  But since that would involve a lot of code changes, we'll
put it off until the broader cleanup effort scheduled for 0.9.0.

After shrinking the global example placeholder size, ones with
additional content within the demo area needed to be tweaked
individually, to prevent the other content from wrapping down or
extending off the side of the container.

The smaller size ensures that the example plots remain fully visible on
more of our most common visitor screen resolutions.

We don't want users to think the example is broken when they first load
it.

The location of the file changed during the recent example revamp.

This prevents the Chicago example from showing up blank.  The
alternative is to define a callback, but that's messier.

This allows a page to have multiple placeholders, since we're no longer
tied to unique IDs.

Fix incorrect display of NaN with the default tickFormatter.

Change-Id: If53fdb1bf9563834c58cf2b569d0e1a6a7155eb8