BaseObject is a class that just handles the Persistent handle attached
to the class instance.

This also removed WeakObject. Reordering the inheritance chain helps
prevent unneeded calls on instances that don't call MakeCallback.

Create a HandleScope before calling the Environment::GetCurrent() that
takes a v8::Isolate* as an argument because it creates a handle with
the call to v8::Isolate::CurrentContext().

CONTAINER_OF was introduced a while ago but was not used consistently
everywhere yet.  This commit fixes that.

Why CONTAINER_OF instead of container_of?  The former makes it crystal
clear that it's a macro, not a function.

Making WeakObject inherit from AsyncWrap allows us to peak into almost
all the MakeCallback calls in Node internals.

Going back to the original names of Wrap/Unwrap now that most all the
class members that duplicate the name and functionality have been
removed.

Switch out to use UnwrapObject from util.h.

The list of supported HTTP methods is available in JS land now so there
is no longer any need to pass a stringified version of the method to the
parser callback, it can look up the method name for itself.

Saves a call to v8::Eternal::Get() in the common case and a costly
v8::String::NewFromOneByte() in the uncommon case.

Expose the list of supported HTTP methods as a property on the 'http'
module object.

Fixes #6422.