As discussed in issue #176, the package has to be built using
$ npm run build
or
$ npm run all
before being able to use it.

Closes #20, closes #79, closes #159

Closes #15, closes #158

Closes  #152

Closes #145

Closes #125

Closes #106

Closes #85, Closes #131

Closes #126

Closes #119

Add JavaScript library that includes an `icons` object, `toSvg` function and `replace` function.

Remove icon categories to simplify npm package.

BREAKING CHANGE: The path to individual SVG files has changed. All SVGs now live on the same level
inside the `icons` directory. For example, `icons/core/home.svg` is now `icons/home.svg`.