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
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.