Change another reference to SenTest to XCTest.
`rake build_docs RELEASE=yes` builds the docs for release.

That means ignoring the private headers, keeping the intermediate files
for post-processing/upload, and not installing the docset (because
the private headers were ignored, but we want to keep their documentation
(if already built) for the developer who's building the docs).

The "private headers" are the following:

* `Sources/**/*+Internal.h`
* `Sources/Classes/Internal/SLMainThreadRef.h`
* `Sources/Classes/Internal/SLAccessibilityPath.h`
* `Sources/Classes/UIAutomation/User Interface Elements/UIScrollView+SLProgrammaticScrolling.h`

as enumerated in the Podspec:
https://github.com/inkling/Subliminal/commit/67e8f7261a214ee8017037fe95a2e5de17345e71#diff-161fa2d1e0140f360679ead8a6c77ab1R19
Fix the index html when building the docs for release.

There are two problems with directly injecting the README into the autogenerated
main index html page:

1. Appledoc can't handle fenced code blocks and some links.
2. Appledoc puts the class hierarchy all the way below the README.

Now, when we build in release, the Rake task will process the index html itself:

1. Using GitHub's Markdown API to render the README, and injecting the resulting
    html itself;
2. Injecting CSS to override Appledoc's stylesheet and float the class hierarchy to
    the left of the README
    (h/t https://github.com/CocoaPods/cocoadocs.org/blob/master/views/appledoc_stylesheet.scss)

This process requires the Nokogiri gem but the requirement will be invoked
only when necessary, i.e. when the docs are built for Release. We only attempt
to fix the index html up when building for Release to speed Debug builds,
to avoid requiring this gem to be installed in general, and because the appearance
of the index probably doesn't matter as much to developers.
Add the version number to the library title as shown on the web.

To clarify when it's updated.

We don't add this in a place that's seen in the docset when in Xcode
because it's obvious when that's updated.
Move screencast information from the README to the Wiki.

For simplicity, also because we'll have the Cocoapods video there too.

Also bring back a link to the API documentation so people don't have to go
looking on the Wiki.
Clarify where Subliminal support can be found.

Hat tip to https://github.com/AFNetworking/AFNetworking/blob/master/README.md#communication
for the idea.
Add to the comparison to UIAutomation.
Add a TOC to the README.
Enable the README code blocks to scroll in the docs index html.
Merge pull request #194 from inkling/jeff/release_docs

Final changes to the docs before 1.1 release.