Enabling Markdown and other JSDoc improvements

This change enables GitHub flavored markdown for APIdoc
comments. The code example in map.js shows how to use markdown
for code snippets. doc/index.md is now included again as start
page for the docs. Everything in the doc/tutorials directory
will also be added to the docs as tutorial. As an example, I
moved the ol3.md file with the architecture to the tutorials
directory.

Currently properties and methods annotated with @inheritDoc
or @override won't be documented at all. This is a known issue,
so I added a custom JSDoc plugin with a hack to avoid this.
Use bootstrap layout and css from examples

I'm sure this can be made much prettier still, but at least we
have a common theme with the examples now.
Making social links work
Use popover from Bootstrap
Creating a resources folder for use by examples and API docs
Use map.on instead of map.addEventListener
Start a maximum of two new tile downloads per frame
Move configuration of maximum tiles loading into map.js
Add goog.base(this) to the MapBrowserEventHandler's constructor
Abort rendering when WebGL context is lost
Merge pull request #469 from twpayne/webgl-context-lost

Abort rendering when WebGL context is lost
Merge pull request #470 from szymonc/error-fix

Add goog.base(this) to the MapBrowserEventHandler's constructor
Correct link to example source
Merge pull request #471 from tschaub/example-typo

Correct link to example source
Update overlay example tags and doc
Quote object keys to prevent renaming in ADVANCED_OPTIMIZATIONS mode
Disable kinetic when multiple touches on screen
Merge pull request #466 from fredj/popover

Use popover from Bootstrap
Remove unused local variable
Merge pull request #474 from fredj/misc

Remove unused local variable