Fixed prior bounds (according to the doc in master branch).

 * Second  and  third  positional  arguments  after the  name  of  the
   estimated  parameter   in  the  estimated_params   block  are  only
   considered in the optimization stage (not in the MCMC)

 * Do not  store bounds  in bayestopt_, because  bounds do  not always
   reflect restrictions implied by prior shapes.

 * prior_bounds routine  returns a structure  (with fields lb  and ub)
   instead of a matrix.