Add search endpoint
Add the commentss request/response builders, model and managers
Making changes according to the code review for comments
Convert search resource to take a builder instead of a query

This enables specifying limit and offset
Merge pull request #53 from box/box-ios-comments

Add the comments request/response builders, model and managers
Merge branch 'search-endpoint'

Conflicts:
	BoxSDK.xcodeproj/project.pbxproj
	BoxSDK/BoxSDK.h
Resolve merge conflicts in xcode project file

Fixes GH-52.
Update iOS and Cocoa README to reflect new endpoint support in v1.2.0