Added 'smart' pointRadius calculator to line graph

core.js
* Split out and documented purpose of magic constant that was being
  used for dynamic padding.

pie.js
* Renamed CENTER, WEDGE_ATTRIBUTES, and PIE_HOLE_ATTRIBUTES to camel
  cased names as the objects they point to are mutable.

line.js
* pointRadius will now be reduced if it is determined that it will
  not fit within its column (xTick) on the graph.

Additional notes
* Added tests for calculatePointRadius.
* Updated failing tests so now all QUnit tests work correctly.
* Updated spacing to be more consistent with JSLint standards.
Merge pull request #5 from gsmith85/calculated-point-radius

Added 'smart' pointRadius calculator to line graph