Support ES modules

[omaraltayyan]

as discussed in #1 this allows this package to be used in webpack

i created a new file that exports the class while keeping the old one for demos

[omaraltayyan]

now what we can do is

import ProtParam from "molecular_weight/src/js/calculation/protparam";

and use this class directly

[ErwinP]

Hi,
I know it has been a long time and I'm not an expert, how how exactly do you serve it into webpack?

Thank you in advance,
Erwin