Squashed commit of the following:

commit 416546e4ee88865b06b7353c8b5ea285595c6b96
Merge: f5a3a62 906eb63
Author: Cody Caughlan <toolbag@gmail.com>
Date:   Fri Feb 28 12:35:25 2014 -0800

    Code cleanup

commit 906eb6346a507c9d994754c1403c86508403fd41
Author: Senthil V S <vss123@gmail.com>
Date:   Sat Mar 1 00:01:13 2014 +0530

    Added more models for batch operations

commit 8727208e9dc01a3164381fb17d5699be6aad6108
Author: Senthil V S <vss123@gmail.com>
Date:   Tue Feb 18 19:50:29 2014 +0530

    Prevented decimal fields with nil value to appear from xml

commit f1ce072d4bda6d37dcf2f7d33039a12a8ce9d139
Author: Senthil V S <vss123@gmail.com>
Date:   Tue Feb 18 17:47:10 2014 +0530

    Added Item to batch request and responses

commit 65e6218307b0a8fce2177c713716feef2ae02a3e
Author: Senthil V S <vss123@gmail.com>
Date:   Tue Feb 4 18:26:38 2014 +0530

    Minor refactorings in accessor names.

commit da7b671ebc484dc57e295ed53d21c4e437559c24
Author: Senthil V S <vss123@gmail.com>
Date:   Mon Feb 3 19:12:56 2014 +0530

    Added BatchResponse and batch service.

commit 6aefd9a3fa0fcec959e84169f300ab55d8951e47
Author: Senthil V S <vss123@gmail.com>
Date:   Mon Feb 3 15:43:40 2014 +0530

    Added 'Quickbooks::Model::BatchRequest'