see https://github.com/colszowka/simplecov/issues/269

Replace use of $stdin.gets with UI.gets

Closes #1644
Closes #1683

Change STDIN to $stdin so it can be reassigned
Use UI.puts instead of print
Add test coverage for Spec#choose_from_array
Fix off by one issue in Spec#choose_from_array

Closes #1675

Add more test coverage for the spec cat command.

This fixes pod lib lint due to Pathname.relative_path_from assuming no
symlinks in path while /tmp is actually a symlink  to /private/tmp

Fix integration test link

Convert the `pod podfile_info` command to a plugin

This removes the podfile_info functionality from cocoapods.

The validation done by `pod spec lint` and `pod lib lint` commands
now checks that all subspecs build independently.

This new behavior can be disabled with `--no-subspecs`.

The validation of a single subspec can be done checked with `--subspec=NAME`.