Fixes #1250.

Lots of people ask about implementing tooltips; hopefully enabling it by
default will help them find it more easily.

These changes were used to test the axis innermost property fix, and
should not have been committed.

It doesn't make sense to calculate the innermost property only when no
tickLength has been provided; the two have little to do with each other.

This way it doesn't inherit from something further up, whose line-height
may be more or less than we expect.

Tweaked the description to indicate that we no longer combine single
slices into 'other', and reduced the threshold from 10% to 5% to
encourage more slices to combine in the demo.

The getTextInfo method previously added new text to the top-level
container when measuring it.  Now it adds the text to the text layer,
just as it will be when rendered, so that parent-child CSS rules can
resolve correctly.

This also avoids having to safe a reference to the top-level container,
since it wasn't used anywhere else.

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.

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.

Give any direct child of demo-containre the same style, so it can be
used for both #placeholder and #overview.

Added explicit border-spacing to compensate for global removal of
padding.  Flot should really take care of this itself; layout-critical
styles shouldn't depend on the user-agent defaults.

Slightly widened the page to account for the fact that most people have
widescreen monitors these days.  Also made text larger and more legible,
and created a nice 'clipping' effect for the placeholder.

To improve organization with the increasing number of examples, every
example page is now the index of its own subdirectory, which contains
all the files specific to that example.

Also fixed formatting and removed unused change to tickFormatter args.