* beautify code block with google-code-prettify
* prettyPrint when componentDidMount
* css style for code block
* skip rule 'no-unresolved' for eslint
* conflict with webpack resolve path
* refactor all code block in example folder with component <Code />
* refactor scss folder structure
* specify the responsibility for each stylesheet with file name
* load local color themes, tomorrow, for google code prettify
* re-select demo color and save into variable
* unify the color system for storybook
* allow user to customize class for header cell
* add corresponding story
* allow user to customize inline-style for header cell
* add corresponding story
* [test] unit test for headerStyle
* [test] unit test for headerClasses
* update Document