Osidb-bindings

Added
- support for nested resources (eg. Flaw references, Flaw comments)
- CRUD operations for Flaw References (create, update, retrieve, retrieve_list, delete)
- CRUD operations for Flaw Comments (create, retrieve, retrieve_list)

Added
- add `next()`, `prev()` and `iterator()` methods for paginated
responses to make page browsing easier
- require exported `BUGZILLA_API_KEY` environment variable for
some session operations which are particulary unsafe (create, update, etc.)
for authentication/authorization against Bugzilla

Changed
- update allowed session operations for each resource

Removed
- remove old aliases for session operations with flaws (eg. `session.retrieve()`,
`session.retrieve_list()`, etc.) in favor of new resource operations
(eg. `session.flaws.retrieve()`, `session.flaws.retrieve_list()`, etc.)

Added
- bring back `session.operation()` as an alias for flaws operations
to prevent breaking changes

Changed
- fix session.status call error