Warnings in YARD

All warnings fixed except the 'undocumentable mixin' warning.
Documented ErrorResponse#on_completion
Improved documentation on KeyOptions#initialize
Documented constants in the Status class
Document Query#ALLOWED_KEYS_FOR_PATH
Document Database#COLLECTION_TYPES
Documented Collection#CONTENT_TYPES and Collection#CONTENT_CLASS
Go to pedantic mode in Inch
Improved documentation on Connection#authenticate_with
There are no Integers in Ruby, only Fixnums
Replace undescriptive variable name in ClientError and ServerError