basiclu_factorize() now calls basiclu_factorize_buckets() with argument
buckets = NULL. Writing a separate interface for factorization with
buckets was necessary to maintain the old API. The implementation has
only been tested through test_factorize() in Julia. In particular rank
deficient matrices have not been tested.

Store # columns that are in any column list in struct lu.ncol_active.
Terminate Markowitz search when # searched columns == # active columns.
This is necessary to avoid traversing all column lists when only a few
columns have been loaded into lists. For example, when the user provides
a column permutation through the buckets argument, then in each
factorization step only one column is loaded into the lists.

Changed license to dual-licensing under GPL v3 and MIT.