Fix issue with Bubble radii

The radius of a point was relative difference between the point and the
smallest point, rather than the absolute radius of the point.

We now use the absolute radius of the point, as well as adding tests and
updating the final diet.
Merge pull request #54 from niksoper/master

Removed .grunt directory.
Make bubble width depend on chart size

For larger charts (with smaller ranges), we can afford to have larger
bubbles. The reverse is true for small charts with large ranges.
Merge pull request #55 from tpkelly/master

Fix bubble chart radii bugs
Merge branch 'upstream'
Colour tweaks to lines and bubbles

- Colour points on line series
- Apply the colour to bubbles.
Fix issue with disappearing bubbles

The bubbles on the app store analysis were being shrunk to tiny dots,
due to the x-axis scale being in 10000s.
Merge pull request #57 from tpkelly/master

Bubble/Point tweaks
Make tick marks default to shown

Previously, tick marks defaulted to 0 width, and were set to 1 everywhere
else. Now, we do the reverse.
Merge pull request #62 from tpkelly/master

Make tick marks default to shown
Added AMD support.
Added checks for dependencies: d3, d3.tip and crossfilter.