Add Pod lib command #850

Tests are still missing.
Merge branch 'master' into lib-subcommand

* master: (59 commits)
  [Bundle] update
  Update CHANGELOG.md
  Release 0.21.0.rc1
  [Gemspec] Update Xcodeproj
  [Bundle] update
  Changelog
  [Bundle] Update
  [Fixtures] Update for release
  [Bundle] Update
  [Rakefile] Examples robustness for future versions of Xcode
  [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
  ...

Conflicts:
	Gemfile.lock
Merge branch 'lib-subcommand'

* lib-subcommand:
  Add Pod lib command #850
Add Pod lib command 2

Closes #850