Use npm shrinkwrap

Lock module dependencies for consistent installs with
[shrinkwrap](https://www.npmjs.org/doc/cli/npm-shrinkwrap.html).

Add ignore file for node_modules/ as the dependencies are shrinkwrapped.

Shrinkwrap created with `npm shrinkwrap --dev` given the nature of the
project.
Merge pull request #3 from uhhs/npm-shrinkwrap

Use npm shrinkwrap
Create README.md
Update index.html
New install instructions to help people get started themselves.

Putting pre-defined list in a code block
Add http-server dependency. Add google analytics code.
Add npm start script
Merge pull request #4 from uhhs/docs-howto-install

New install instructions to help people get started themselves.
Readme changed
Fix broken link to github repo
New level writind format: jsrl
Changed keyword directions level
Update README.md
Update README.md
Update README.md
Add advanced levels group
Fix passed levels highlight
Add 13 level
Fix levels imiidiate change bug
Fix level 13 text