Merge pull request #49 from p0deje/master

Release v1.3.0
fix 18th sample
update docs for Document and Request
updated EntitfyFields
Role#can* methods are now boolean
updated Signature
added Field#acceptable_values
added Envelope#is_demo
added :scheduled status for Enveloped
added Envelope#delegate_recipient!
added FieldMethods#assign_field!
added Envelope#signed_document!
DocumentMethods#documents! should find documents both by :documentId and :id
added Contact#add_integration!
support watermarks in Signature::Form
Signature::Form now has document methods
added Form#fields_in_final_file_name
updated Form#create!
support field methods in Signature::Form