new features expected

[craigstar]

First, thank you for your contribution! This is amazing using sophus in python!
However, there are couple of useful features that I think its necessary.

1. SE3(R, t) # create Instance from R, t
2. setTranslation() # I don't know why T.trans(x, y, z) just return me correct translation but with identity rotation. This is a bug I guess. Also, I want to change translation in place.