Added github flavored markdown syntax highlighting to code blocks

Pretties up the code examples in the docs.

example on line 42-57 with syntax highlighting:
````js
/**
 * Set project info
 */
project: {
  src: 'src',
  app: 'app',
  assets: '<%= project.app %>/assets',
  css: [
    '<%= project.src %>/scss/style.scss'
  ],
  js: [
    '<%= project.src %>/js/*.js'
  ]
}
````
Not applied to the last two command line code blocks because there is no syntax highlighting available. Should have been included in #12, but I forgot...