rename Question to ExternalQuestion

Conflicts:
	spec/operations/create_hit_spec.rb
QuestionForm (aka Internal Question) and a new question_form setter on the CreateHIT operation
brief docs for QuestionForm feature
use UTC and ISO8601 format for the timestamp
rename 'note' to 'annotation' for consistency with response and with its real name (RequesterAnnotation)
rename 'assignments' accessor/mutator to 'max_assignment' for consistency with its real name (MaxAssignments) and to remove confusion between it and the other property named 'assignments'
rename 'auto_approval' to 'auto_approval_delay' for consistency
use tap instead of inject to build an array (higher performance, cleaner code)
don't swallow method_missing
add 'question' field to Hit response; allow QuestionFormBuilder to take either a QF or just its content; fix another method_missing problem

Conflicts:
	lib/rturk/parsers/responses/get_hit_response.rb
add mechanical turk master qualifications
Amazon Master qualification ids vary between sandbox and real environments - see https://forums.aws.amazon.com/thread.jspa?threadID=70812
Amazon Master qualification ids vary between sandbox and real environments - see https://forums.aws.amazon.com/thread.jspa?threadID=70812

Conflicts:
	lib/rturk/builders/qualification_builder.rb
use amazon-master-aware 'types' method instead of 'TYPES' constant

Conflicts:
	lib/rturk/builders/qualification_builder.rb
allow ':exists => nil' in qualification

Conflicts:
	lib/rturk/builders/qualification_builder.rb
add link to Mark's talk to README
actually, not all the API calls work
add pagination response fields
use Erector for QuestionForm and AnswerKey builders

Conflicts:
	Gemfile
Fix merge conflict on gemspec deps