Code cleanup: remove diagnostic print statements
Update 404 handling; implement and test DELETE RO
Yak shaving: created utility for mocking ROs for testing, using httpretty
Basic Overlay RO tests now passing (still need to do live tests)
Updated formatting
Add .png format for minim results model
Fix up base URI used when parsing RO manifest
Refactored ROSRS_Session to use HTTP_Session, and added logic to support external servers
Bug fix handling of baseuri and exthost parameter
Fixes to allow RO to reference external annotations
Refine RO deletion for test suite
Fixed bug in refactored code for reading RDF ater following redirects
Add screenshots of roverlay inaction, for documentation
Re-enable HTTPSession functionality; fix up tests - all tests pass
Clean up code
Bump version number to 0.2.15
Refactor spreadsheet grid access to a separate module
Updated mkminim to generate Minim direct from XLS filer (uses xlrd)
Bump mkminim version number (direct Excel support)
Add context protocol to HTTP_Session class