add docs about the docs

Closes #636, closes #639
Bootstrap compat: support `offset(coordinates)`

References #642
Bootstrap compat: implement `detach()`

References #642
work around Chrome bug where Ajax callback fires more than once

The bug is present in Chrome 23.0.1271.64 and possibly iOS 6, and is
reproducible using the debugger but otherwise occurs randomly.

References #633

http://code.google.com/p/chromium/issues/detail?id=159827
fix $.isPlainObject() for `window` in Opera

Fixes #652
$.ajax error callback correctly reports "abort" status

Before it was just "error".

Assumes that an XHR status of "0" means that the request has
been aborted.

Fixes #649
additional test case for $() fragment with properties

Proves that Zepto behaves differently than
http://bugs.jquery.com/ticket/12881
fix `hasClass` in collections of multiple elements

It should return true if *any* of the elements has the class, not just
the first one.

Fixes #631
avoid explicit uses of `undefined` where possible
avoid another use of `undefined`
exec phantomjs
stop iteration in fn.each() when the callback returns false

This makes it compatible with jQuery and current Zepto documentation.
add few missing tests for collection returning self
Ajax: add ability to set `xhr()` factory per-request
have get() method accept negative index
fix assertion order in `get()` tests
support for multiple class names in toggleClass()
refactor toggleClass and tests
Add os.phone and os.tablet (booleans); Detect Firefox mobile, PlayBooks
Add Windows Phone/Windows RT user agent strings for prosperity (Zepto doesnt support IE 10)