[Pod::Command::Spec] added `pod spec lint all' / improved linting
[Pod::Command::Spec] added `pod spec lint all' / improved linting

- `pod spec lint all' allows to view the warnings and
  the deprecation notices of all repos. If a podspec
  does not validate the informative is not captured
  and breaks the flow.
- added support for deprecation notices
- added `config.ios?' and `config.osx' deprecation
  notice

Ashton-W/CocoaPods,mglidden/CocoaPods,0xced/CocoaPods,vivekshukla-mob-ibtech/Repository,ashfurrow/CocoaPods,mglidden/CocoaPods,mglidden/CocoaPods,orta/CocoaPods,segiddins/CocoaPods