Added GTMNSString+XML, GTMURLBuilder, and their dependencies.

These are taken from Google Toolbox for Mac:

svn co http://google-toolbox-for-mac.googlecode.com/svn/trunk/ google-toolbox-for-mac-read-only
    r610
    Copyright Google Inc.
    Apache 2.0 license.
Added NSData+Base64 from FoundationAddition.

git://github.com/yllan/FoundationAddition.git
c6017da2198c99730cbe41baa2db3aa2862d2abb

//  Created by Matt Gallagher on 2009/06/03.
//  Copyright 2009 Matt Gallagher. All rights reserved.
//
//  This software is provided 'as-is', without any express or implied
//  warranty. In no event will the authors be held liable for any damages
//  arising from the use of this software. Permission is granted to anyone to
//  use this software for any purpose, including commercial applications, and to
//  alter it and redistribute it freely, subject to the following restrictions:
//
//  1. The origin of this software must not be misrepresented; you must not
//     claim that you wrote the original software. If you use this software
//     in a product, an acknowledgment in the product documentation would be
//     appreciated but is not required.
//  2. Altered source versions must be plainly marked as such, and must not be
//     misrepresented as being the original software.
//  3. This notice may not be removed or altered from any source
//     distribution.
Added base64EncodedData.
Added.
Added.