Add a smoke test for the iOS static lib

We tried to implement this as a separate target inside the existing
Cedar project, but found that XCode 5 has multiple problems adding a
new target for iOS to this project. I suspect it has something to do
with the project having been upgraded from earlier versions of xcode.

It would obviously be best if this was a separate target, but Jesse and
I spent a long time hitting our heads against a wall trying to make that
work, and it seemed like adding this as a separate, standalone project
was the most valuable use of our time on this task.

We tested locally that when a header isn't included in the iOS staticlib
target that the rake task will return a non-zero exit code, so this
should make accepting PRs that run on Travis a lot easier.

NB: this is going to fail on Travis because we branched at a ref where
ConformTo.h is not included in the framework target. We considered rebasing
to show that it would go green, but we thought the fact that it does go red 
in this case was valuable information to share.