Create lightweight HydraValue model
Move entity modules to hydra_entity namespace
Create lightweight model implementation

HydraAttribute::Model is a lightweight representation
of ActiveRecord::Base model
Remove database_cleaner gem
Try to resolve travis' issue "syntax error" during performing sql query

Seems it cannot perform multi-insert query
Add auto generation attribute methods for HydraAttribute::Model
Add tests for identity map

- HydraAttribute::IdentityMap
- HydraAttribute#identity_map
- HydraAttribute::Model::IdentityMap
Add possibility for creating nested indentity map objects
Add #save method for Model
Create Mediator for observing models
Raise an error when couldn't find a record
Use callbacks for CRUD actions
Add tests for destroy method
Merge branch 'master' into value_model_optimization
Merge branch 'master' into value_model_optimization
Remove Appraisal gem
Resolve dependencies between rspec and cucumber
Try to resolve problem with travis
Try to resolve travis problem wit gemfile via env
Debugging travis