Added the ability to query existing instances of the model for an instance with the specified identifier

 + (instancetype)existingModelWithIdentifier: (id)identifier;
Added the ability to query existing instances of the model for an instance with the specified identifier

 + (instancetype)existingModelWithIdentifier: (id)identifier;
Moved code into the Static Methods section.

Added the ability to query existing instances of the model for an instance with the specified identifier

 + (instancetype)existingModelWithIdentifier: (id)identifier;
Merge branch 'master' of https://github.com/robinsenior/FDModel