Add ARC workaround for be_nil and be_same_instance_as matchers.

[Fixes #46780343]
Added ARC specs to iOS target. Added more examples.

reinterpret_cast expectedValue_ for be_same_instance_as.

Examples now cover __strong & __weak objects.
Merged with latest master.

master-ref: 011db95e5425fd20ade3ae00b1a652b2af2f7f64

Conflicts:
	Cedar.xcodeproj/project.pbxproj
Merge pull request #123 from jeffh/arc

Added ARC support (fixed ARC-related errors for be_nil and be_same_instance_as matchers).