Reports, User ID Fix, README Improvements

[pswaminathan]

• Add module for Reports API metadata and data
• Fix user ID/session ID variable-setting with cookie auth
• Use next instead of six.advance_iterator as I have already committed to Python >=2.7
• Rename constants to utils (constants is never exposed externally anyway)
• Rename T1XMLParser to XMLParser to fit with the theme of not prefixing everything with T1
• Clean up some whitespace
• Overhaul README to include examples, explanations, method signatures for important methods
• Add Contributors file

[pswaminathan]

Reports fixes #10