Adding Generators and Inherit Tags

• Added Generators for pagination
• Added the ability to inherit tags from the queue or connection object
• Edited README for tags usage
• Added a method get_measurements
• Added the ability to use environment vars when creating a new connection

MD support and pep8 fixes

This release introduces new methods to submit and query multidimensional data streams to Librato, and makes the code pep8 compliant.

Allow arbitrary Stream attributes; 403 error parsing

Formally adds Stream#gap_detection attribute and also avoids throwing an exception for new/unknown Stream attributes that come back from the API by setting properties for those generically.

Also fixes a bug with error parsing on rate limiting (http 403) errors.

#122
#124

Support color attribute on Stream

Allows Stream#color to be set (if it comes back from the API)

Add attributes to Service model

#117 to add title, type, and settings to Service model, and add a list_services() method.