A L8Runtime can now actually be deallocated. Verified use of GetCurrentContext() in callbacks.

Because of the strong reference to the WrapperMap, and the WrapperMap containing a strong reference to the Runtime, plus the strong reference in the v8::Context, a Runtime would never deallocate. #1.
The use of GetCurrentContext() on the Isolate is correct, as in callbacks, the current context is always the context the callback came from. #5. (v8-users mailing list)
Remove unavailable L8Value methods. Fix L8Value documentation. Make -[L8Runtime executeBlockInRuntime:] deprecated. Property-ize V8Value, V8Isolate and V8Context methods.
Use dot notation for -[L8Value V8Value].
Un-deprecate -[L8Runtime executeBlockInRuntime:]; providing context everywhere is harder than it seems.
Rename L8Runtime to L8Context, to match the JSC API even closer.
Make doxygen ignore __attribute__s, because it throws warnings on them.