Add --repo-update option

Closes https://github.com/segiddins/cocoapods-dependencies/issues/5
Don't inspect or try anything related to integration

Closes https://github.com/segiddins/cocoapods-dependencies/issues/6
Allow user to supply a podspec/pod to determine dependencies

Closes https://github.com/segiddins/cocoapods-dependencies/issues/4
Release v0.3.0