fix default exports, use jsx components

[laggingreflex]

This does two things:

• Simpler syntax: export { default as Button } from './Button/Button.jsx';

• Uses Button/Button.jsx instead of Button/index.js (which is created by compileComponents.js). It lets you run webpack --watch without compileComponents.

[prateekbh]

I totally agree about adding a simpler syntax to main index.js.
But there is a reason why I import that from index.js and not particular Component.jsx.
Imagine you are using building a project, which works absolutely fine, then you add preact-material-components.

Suddenly you realize that to use these components, you'll need to change your webpack config or gulp config or something as they use some more stuff from ES6/7/.... This might become frustrating for anyone using these, hence I compile Component.js to a basic ES6 file and put them in index.js.

For people using ES5 a UMD version is kept in dist under main key.
And using module key a basic ESM version is pointed to all index.js

[prateekbh]

I also totally support that compileComponents should become part of webpack process itself, May be we can just create a small webpack plugin out of it just like I did for CssMigrationWebpackPlugin