Lazy load entity and repository

Additonally, adding validation for presence of entity and repository for load!
Merge pull request #106 from joneslee85/lazy-load-entity-and-repo

Lazy load entity and repository + presence validation of entity and repo on load
Bump version to v0.2.0.dev
Lotus::Model.configure to return self
Fix bug in memory adapter offset

Before this fix, offset(n) returned the last n records, while it should
return all records except for the first n records
Merge pull request #109 from rhynix/memory_adapter_offset_fix

Make Memory::Query#offset behave like SQL