Make the TOC automatically

The TableOfContents component creates the TOC of the page based on headers
automatically. Currently, the TOC for only the Guide page experimentally, but
it should be reusable for other pages if needed. And the max depth of the TOC
is customizable.

Resolve #84.
Fix a typo in React page
Merge pull request #123 from okuryu/fix-react

Fix a typo in React page
Merge pull request #122 from okuryu/toc

TOC
Add docs on how to load locale data

This adds back the docs on how to load the locale data onto the page
for each integration.

Closes #121
Merge pull request #124 from ericf/load-locale-data

Add docs on how to load locale data
Add analytics to site
Merge pull request #125 from ericf/analytics

Add analytics to site