0.18.0

Enhancements

• [PlistHelper] The native extension has been removed in favour of the usage of
  the plutil tool to read ASCII property list files.
  Fabio Pelosin
  Xcodeproj#168
  Xcodeproj#167
• [PBXFileReference] If a file reference represents an external Xcode project
  and is removed from the project then all items related to the external
  project will also be removed.
  JP Simard
  Eloy Durán
  Xcodeproj#158
  Xcodeproj#161

Bug fixes

• [Workspace] Fixed adding a project to a workspace.
  Alessandro Orrù
  Xcodeproj#155