Simplified code of Black Scholes formula in some limit cases. Improved JavaDoc.

git-svn-id: http://svn.finmath.net/finmath%20lib/trunk@778 48fcbb9e-5639-0410-8b25-842128a4905d
Simplified RandomVariable factory provided by the model.

git-svn-id: http://svn.finmath.net/finmath%20lib/trunk@779 48fcbb9e-5639-0410-8b25-842128a4905d
Added some more elementary tests for the RandomVariable.

git-svn-id: http://svn.finmath.net/finmath%20lib/trunk@780 48fcbb9e-5639-0410-8b25-842128a4905d