<rdar://problem/15540121>

This consists of three main changes:
1) Converting the return type of initializer methods to instancetype.
2) Declaring properties rather than getters and setters.
3) Tagging C API methods with information about their memory management semantics.

Changing the declarations from getters and setters to properties also required
updating the headerdoc in a number of places.

Reviewed by Anders Carlsson.

* API/JSContext.h:
* API/JSContext.mm:
* API/JSManagedValue.h:
* API/JSManagedValue.mm:
* API/JSStringRefCF.h:
* API/JSValue.h:
* API/JSVirtualMachine.h:
* API/JSVirtualMachine.mm:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160454 268f45cc-cd09-0410-ab3c-d52691b4dbfc