Closes #1160

Closes #1157

See #1152

fix for erroneous linting on 0.21.0.rc1

- let spec in "validates a podspec with dependencies" validate
- fixed a bug in `write_podspec`

* dedicated-targets: (49 commits)
  [CHANGELOG]
  [Generator::Xcconfig] Docs
  [Bundle] Use Xcodeproj from master
  [Installer] Rename #targets to #aggregate_targets
  Add files which were creating issues with git
  Delete files creating issues with git
  Update integration test fixtures
  Case change for case-sensitive file systems
  Update tests
  Move method below attributes
  Add spec_consumers to targets for xcconfig file
  Add default_ld_flags method
  Fix developer framework path
  Restore storing native target in target
  Fix accessor naming libraries -> pod_targets
  [Specs] Fix require paths
  XCConfig is generated for Pod targets as well
  Create a single PodTarget for all subspecs
  Fix old target methods naming
  [TargetInstaller] Minor clean up
  ...

Conflicts:
	Gemfile.lock

* master:
  [Spec] Rebuild integration test fixtures.
  Use a different resources-to-copy.txt file for each target
  Grammar fix in CONTRIBUTING file
  Made SO link to our search query
  [CONTRIBUTING] Add back links to ML and SO. Thanks @secboffin.
  [CONTRIBUTING] Make it even clearer/simpler. Thanks to @Manfred.
  [CONTRIBUTING] Try to be as clear as possible about do's and don'ts.

Conflicts:
	spec/integration/install_add_pod/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_add_pod/after/execution_output.txt
	spec/integration/install_custom_workspace/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_custom_workspace/after/execution_output.txt
	spec/integration/install_external_source/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_external_source/after/SampleApp.xcodeproj.yaml
	spec/integration/install_external_source/after/execution_output.txt
	spec/integration/install_local_source/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_local_source/after/SampleApp.xcodeproj.yaml
	spec/integration/install_multiple_targets/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_multiple_targets/after/SampleApp.xcodeproj.yaml
	spec/integration/install_multiple_targets/after/execution_output.txt
	spec/integration/install_new/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_new/after/execution_output.txt
	spec/integration/install_podfile_callbacks/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_podfile_callbacks/after/execution_output.txt
	spec/integration/install_podspec/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_podspec/after/execution_output.txt
	spec/integration/install_remove_pod/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_spec_callbacks/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_spec_callbacks/after/execution_output.txt
	spec/integration/install_subspecs/after/Pods/Pods.xcodeproj.yaml
	spec/integration/install_subspecs/after/SampleApp.xcodeproj.yaml
	spec/integration/install_subspecs/after/execution_output.txt
	spec/integration/update/after/Pods/Pods.xcodeproj.yaml
	spec/integration/update/after/execution_output.txt