Added method Ray.intersectSphere(sphere) and 3 semicolon insertions to Ray.js

As brought up in issue https://github.com/mrdoob/three.js/issues/4801

Changed this method to reflect the functionality of @bhouston 's original Ray.js .

Now this method looks like:
THREE.Ray.intersectSphere( sphere, optionalTarget );

It returns null if no intersection is found, and if a collision is found, it returns a THREE.Vector3( ) containing the location (x,y, and z coordinates) of the contact point in world space.

Here's a demo showing off the new feature:
http://erichlof.github.io/AsteroidPatrol3D/RayIntersectSphere.html

and the demo's source to see how it's used:
https://github.com/erichlof/AsteroidPatrol3D/blob/gh-pages/RayIntersectSphere.html

Also, 3 minor semicolon insertions were made to Ray.js 

@mrdoob @WestLangley @bhouston
Update: I added 9 tests on this method in the unit tests folder per WestLangley's request.  I kept the structure, whitespace, and functionality the same as bhouston's.   All 9 tests pass.  :)

Thanks!