* Added getRandomConfiguration, which generates a random configuration for a manipulator. Returned configuration is within joint limits for 1-dof joints, if they're set, and uses a uniform distribution on SO(3) and Gaussian distribution on R^3 for floating joints.
* fixed some tests that were simply using randn to generate random configurations. This would result in quaternions that weren't unit length... Now using getRandomConfiguration
* added dHdq: partial derivative of vec(H) with respect to q, where H is a homogeneous transform. Can possibly be made more efficient.
* added a few new tests