Document multiple ways to insert comments in JSX
Update 05-reusable-components.md

`any` also seems to accept primitive values, not only objects. And since we already have `React.PropType.object`, the description was confusing.
fix typo in 09.4-test-utils.md
docs remove comment section
Carry ajax error checking from step #13 forward to other ajax steps

The following steps also have an ajax function, but the 'error:' param
is gone after #13:
#14
#17
#19
#20
This may be superfluous, but it helped me find an error with something I
was doing - Namely, in my .json file, I had single line javascript
comments ("//") that I copied from the tutorial. I couldn't find the
issue on later steps, but was able to see my issue when the error
handler complained about an unexpected "/" in my file in step #13.
Update tutorial.md
Update refs example code to use onChange

Fixes #1408.

Test Plan: Copy each code snippet into jsbin; type in the text box successfully; click the button and see the input clear (and in the second example, get focused).
Fix preposition capitalization
Match `setTimeout` delay with documentation
Update videos.md
Move tooling info to Complementary Tools wiki

I moved the info that was here to the wiki page: https://github.com/facebook/react/wiki/Complementary-Tools; it doesn't need to live in the website any more.
Update jsfiddles in thinking-in-react to remove onSubmit from forms
link to tagtree 'Thinking in React' video
Fixed a couple of issues with link to tagtree.tv video
Embed video from F8

Edited in githubs inline editor. Not tested!
Fixed incorrect usage of github api in example

more: https://developer.github.com/v3/gists/#detailed-gist-representation
Title case on videos page
Move tagtree image to docs/

Missed this in #1470