use of delegators and Forwardable, thought this is not inheritance removal

Signed-off-by: Christian MICHON <christian.michon@gmail.com>
removal of @trees, using instead pure MapDB functionality

Signed-off-by: Christian MICHON <christian.michon@gmail.com>
Merge branch 'master' with @trees refactoring; kept instance_variable_set over instance_eval

Signed-off-by: Christian MICHON <christian.michon@gmail.com>