Support usage as HOC for decorating class components

[eliperelman]

Fixes #8.

[eliperelman]

I also tested this out in the demo by replacing:

const App = epitath(function*() {
  console.log('Rendering again!');

with:

const App = epitath(class Demo extends React.Component {
  * render() {
    console.log('Rendering again!');

[fakenickels]

Thanks @eliperelman, added some comments and after that we're good to merge

[eliperelman]

@grsabreu done!

[fakenickels]

Thanks for your contribution @eliperelman , I'll be updating the project contribution soon!

[eliperelman]

Sounds great, thank you!