Add vee

[artivis]

Add 'vee', the API is shown in the following pseudo-code:

LieAlg lie_alg = Tangent::Random().hat();
---
Tangent tangent = Tangent::Vee( lie_alg );
// or
tangent.setVee( lie_alg );

[joansola]

Hey. Just one small comment on a "bracket" thing.

[joansola]

OK