Add the ability to order tests by run group.

See the documentation on `+[SLTest runGroup]`.
Remove TRAVIS environment variable from .travis.yml
Merge pull request #172 from MaxGabriel/patch-3

Remove TRAVIS environment variable from .travis.yml
Allocate pixels with all zero components for bitmap context

We should use calloc here instead of malloc to ensure that the
pixel buffer we use for testing visibility is all clear when
nothing has been drawn yet.  This can be an issue in cases where
renderViewRecursively doesn't actually draw anything.  If nothing
is drawn then this function should return 0, but if we're unlucky
with the random values in the malloced pixel buffer we might see
something "drawn" in the pixel buffer anyway and return non-zero.
Merge pull request #175 from inkling/aegolden/clear_pixel_buffer

Allocate pixels with all zero components for bitmap context
Merge pull request #162 from inkling/jeff/run_group

Add the ability to order tests by run group.
Include collection view cell mock views in accessibility paths. (fixes #178)
Update the SDKs supported in CI.

It's not technically correct to say that 7.0 is no longer supported _at all_,
but we remove it from the list because we don't plan to test against it in CI.

We remove 5.1 because Travis no longer supports 5.1.
Add some missing escapes in `subliminal-test`'s documentation.
Use `instruments`' `-w` flag to enforce the simulator SDK & device type. (resolves #143)

This capability, added in Xcode 5.1, obviates the need to enable/disable
SDKs to force `instruments` to use a particular SDK for testing
(http://openradar.appspot.com/radar?id=3107401) and the need to
specify the `TARGETED_DEVICE_FAMILY` argument to force `instruments`
to use a particular device family for testing
(http://openradar.appspot.com/13607967).

The first components of the configurations respected by the `-w` flag
(the device types) are the same as the items listed in the iOS Simulator's
"Hardware -> Device" menu, so `subliminal-test` remains
backwards-compatible, despite its documentation changing.

Some references to iOS 5.1 have been updated in preparation for our
eventual dropping of 5.1 support (though we still do support it currently).
Deprecate the `--live` and `-login` password options of `subliminal-test`. (refs #176)

`instruments` may (and should) be "pre-authorized" using the instructions
at https://github.com/inkling/Subliminal/wiki/Continuous-Integration#faq.
Remove the `before_install` step from `.travis.yml`.

Travis initializes submodules for us as described here:
http://docs.travis-ci.com/user/build-configuration/#Git-Submodules
Don't try to unlink `appledoc` on Travis.

It's not (yet?) installed on the new 10.9 boxes.
Install `appledoc` from binary on Travis.

appledoc 2.1 uses GC and so cannot be compiled using Xcode 5.1,
so we download a pre-built version from the `gh-pages` branch
and manually install it.

The version was pre-built following the instructions [here][1] using
Xcode 5.0.2 and the `appledoc21` formula. I thought that maybe we
could install the resulting bottle [directly][2] but for some reason that
fails.

[1] https://github.com/Homebrew/homebrew/wiki/Bottles
[2] https://github.com/Homebrew/homebrew/wiki/Bottles#local-bottle-usage
Ensure Travis uses the latest version of `xctool`.

`xctool` 0.1.14 will fail to run Subliminal's unit tests.

Travis is supposed to have 0.1.15 installed--see
https://github.com/travis-ci/travis-ci/issues/2051#issuecomment-40817341.
Update the "terminal evaluation delay" for Travis' new VMs.
Merge pull request #181 from inkling/jeff/new_instruments

Update `subliminal-test` to take advantage of `instruments` 5.1.
WIP: Contributing guidelines. (refs #82)

WIP, so [skip ci]
Flesh out contributing guidelines (Resolves #166) [ci skip]
Remove "Feature Requests" section for now