Added Rugged, converted existing Grit code

Description incomplete, coming :soon:  

Here's a [Working demo](http://glittergallery-ropaku.rhcloud.com/) and a [Test Project](http://glittergallery-ropaku.rhcloud.com/rohitpaulk/TestProject1) that I set up.
Ha. Found the problem. It was in the different versions of rugged that we were using, my bad. 

Here's the target method in rugged v0.19.0: 

```c
/*
 *  call-seq:
 *    reference.target -> oid
 *    reference.target -> ref_name
 *
 *  Return the target of the reference, which is an OID for +:direct+
 *  references, and the name of another reference for +:symbolic+ ones.
 *
 *    r1.type #=> :symbolic
 *    r1.target #=> "refs/heads/master"
 *
 *    r2.type #=> :direct
 *    r2.target #=> "de5ba987198bcf2518885f0fc1350e5172cded78"
 */
static VALUE rb_git_ref_target(VALUE self)
{
	git_reference *ref;
	Data_Get_Struct(self, git_reference, ref);

	if (git_reference_type(ref) == GIT_REF_OID) {
		return rugged_create_oid(git_reference_target(ref));
	} else {
		return rb_str_new_utf8(git_reference_symbolic_target(ref));
	}
}
```

And here's the same in the current version - 

```c
/*
 *  call-seq:
 *    reference.target_id -> id
 *    reference.target_id -> ref_name
 *
 *  Return the target of +reference+.
 *
 *  If +reference+ is a symbolic reference, it returns the target
 *  reference object.
 *
 *  If +reference+ is a direct reference, it returns the target object.
 *
 *    ref1.type #=> :symbolic
 *    ref1.target #=> #<Rugged::Reference ...>
 *
 *    ref2.type #=> :direct
 *    ref2.target #=> #<Rugged::Commit ...>
 */
static VALUE rb_git_ref_target(VALUE self)
{
	git_reference *ref;

	Data_Get_Struct(self, git_reference, ref);

	if (git_reference_type(ref) == GIT_REF_OID) {
		git_object *target;

		rugged_exception_check(
			git_object_lookup(&target, git_reference_owner(ref), git_reference_target(ref), GIT_OBJ_ANY)
		);
		return rugged_object_new(rugged_owner(self), target);
	} else {
		git_reference *target;

		rugged_exception_check(
			git_reference_lookup(&target, git_reference_owner(ref), git_reference_symbolic_target(ref))
		);

		return rugged_ref_new(rb_cRuggedReference, rugged_owner(self), target);
	}
}
```

Also one thing that I just noticed is that - 0.19.0 is like a year old, and it [only supports Ruby 1.9](https://github.com/libgit2/rugged/releases/tag/v0.19.0). Considering that one main reason behind us changing to Rugged is that we wanted Rails 4 and Ruby 2 support... Do you think that we should just bundle the development branch?