Added documentation for n_sqrtmod_2/primepow.
Added documentation for n_sqrtmod_2/primepow.

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