Add SPM support

[alexandre-pod]

Added

• Add support for Swift Packages
  • Add new optional variable nammed "project_type" which accepts 2 values: "xcode" and "spm". When missing ccios use "xcode" by default.
  • When "project_type" is set to "spm" ccios will not try to update a pbxproj and will only generate files.
  • When "project_type" is set to "spm" multi target definition is no longer supported for generated files, as this is not supported by SPM.
  • When generating files for an spm project, the target name in the header is either: the target defined in the template variables, the target defined in .ccios.yml, or it will guess the name of the target when your package uses the standard naming scheme of: "Sources/<target_name>/".