Modified the comments for the limb multiplication function and added my copyright to the file.
Modified the comments for the limb multiplication function and added my
copyright to the file.

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