Convert Batch Scripts to use ShellJS

[frastlin]

Hello,
Currently the batch scripts are not cross-platform. It is extremely easy to make them cross platform with a library called shellJS.
This will also fix:
#45
For example, here is the build script using shellJS:

var path = require('path');
var shell = require('shelljs');

console.log('Building...');
shell.rm('-rf', path.join(path.resolve('.') + 'docs'))
shell.exec('hugo')
shell.exec('sw-precache --root=docs && git add -A', function(error, stdout, stderr) {
  if (error !== null) {
    console.error(error);
    return;
  }
  console.log('Site built at /docs.');
});