Fix issue #61
Merge pull request #61 from lldong/support-nil-target

ASControlNode not sending action to the responder chain when target is nil
Update CONTRIBUTING.md
Tweak .gitignore.
Fix ASImageNode docblocks.

(#64, #65)
[appledoc] Include subclassing header.

Use `--no-merge-categories` to prevent subclassing-only documentation
from appearing in the general API reference.  Use consistent category
names.
[appledoc] Include ASRangeController.
[appledoc] Enable explicit crossrefs.

Fix warnings for existing `@see ...` crossrefs.
[appledoc] Fix all appledoc warnings.  (#65)
[appledoc] Document ASCellNode.
Add REQUIRES_SUPER annotations.

Closes #51.
[appledoc] Fix hierarchy / memory docblocks.
Add -didExitHierarchy internal hook.
Fix ASDisplayNodeScreenScale() warning.
Use ASDisplayNodeScreenScale().

ASImageNode and ASHighlightOverlayLayer were both using
[[UIScreen mainScreen] scale] directly.  Bad.  No cookie.  Use
ASDisplayNodeScreenScale() instead.

(Also, regenerate Xcode project with Xcode 6 and current CocoaPods.)
Remove ASImageNode thread affinity asserts (#57).
Improve ASRangeController dealloc-safety.

(1) We can't size nodes without a delegate, and if our owning controller
has been deallocated, our delegate will be nil.  Handle this more
gracefully.

(2) Our teardown code needs to be executed on the main thread, but it's
conceivable that we might hit refcount 0 on a background queue.  Force
deallocation to occur on the main thread.

Closes #27.
Fix #67
Static library support (fixes #54).
Update landing page.