Vector 3 fixes

- Make x,y,z fields public
- Add instance dot product and cross product methods. The static dotProduct() and crossProduct() functions are now deprecated.
- Add lerp and +, -, *, / operations
- Add Vector3.zeroVector
- Add == operator that compares the Vector3 to a scalar. equalToScalar() is now deprecated.
- Add unit tests

Thanks for @dghost for these improvements.