Adds cursor-based pagination capability to support GraphQL-Relay style. Single column ordering only supported.
Breaking changes
* All repository and unit of work related resources are now available in `sqlalchemy_bind_manager.repository` module and not anymore in `sqlalchemy_bind_manager` base module
* Pagination information for `PaginatedResult` are now grouped in a nested `PageInfo` object in the `PaginatedResult.page_info` property.
* `per_page` and `items_per_page` occurrences have been consolidates as `items_per_page`
Non-breaking changes
* `BaseRepository` moved to its own module
* Presenter classes added to produce `PaginatedResult` and `CursorPaginatedResult`
* Default `paginated_find` to page 1