Initial implementation of xgcd based hnf that returns the associated transformation matrix too.
Initial implementation of xgcd based hnf that returns the associated transformation matrix too.

jpflori/flint2,jpflori/flint2,dsroche/flint2,dsroche/flint2,dsroche/flint2,wbhart/flint2,jpflori/flint2,dsroche/flint2,fredrik-johansson/flint2,jpflori/flint2,fredrik-johansson/flint2,fredrik-johansson/flint2,wbhart/flint2,wbhart/flint2