Add default value

Change documentation
Add default value for direct mapping
Add test for keypath regression
Catch key path exceptions
++xcconfigs
Merge pull request #267 from MantleFramework/xcconfigs-bump

Bump xcconfigs for Xcode 5 backwards compatibility
Fix spec description
Merge pull request #266 from MantleFramework/keypath-regression

Keypath regression
Check if model is a placeholder before we override existing CoreData properties
Add a workspace for standalone development.
Pull dependencies from the workspace.
Scheme version bump.
Document the workspace.
Merge pull request #279 from MantleFramework/flatten-dependencies

Flatten dependencies
Throw an error if JSON mappings to match property keys
Revert "Check if model is a placeholder before we override existing CoreData properties"

This reverts commit 0c52681f3648d93ccb8419f70ba7427dfd7c6502.
Merge branch 'master' of github.com:MantleFramework/Mantle into hack/check_if_placeholder_before_overwriting_coredata
MTLManagedObjectSerializing now allows merging values before overwriting
them.
Added convenience functions for arrays of JSON/Models

You can now use [MTLJSONAdapter modelsOfClass: fromJSONArray: to convert an array of JSON dictionaries to models and then [MTLJSONAdapter JSONArrayForModels] to get a JSON array of dictionaries from a array of models.  Closes #176.
A bit of documentation clean up
Code cleanup in response to PR comments