Radically reduce first run pod setup bandwidth.

Given that Cocoapods doesn't need the history of the Specs repo we can radically improve the initial setup time by only checking out HEAD. This reduces the initial download from >200MB to roughly 3.5MB, a massive win for folks with slow interwebs.

git pull/git fetch+git rebase work as expected.
Update CHANGELOG.
Merge pull request #1803 from jverkoey/fastsetup

Radically reduce first run pod setup bandwidth.
[Command] Add `pod repo add --shallow` option. Default to false.
[Command] Setup shallow clones by default or use `--no-shallow`.
[Command] Setup full clone when using `--push`.
[CHANGELOG] Expand on shallow repo clones.
Uniformize spec template quotes
Uniformize spec template double quotes
Merge pull request #1819 from vtourraine/master

Uniformize spec template quotes
Spec documentation: Address should be singular
Search: Present a user friendly message with invalid regex

Fixes #1821
`pod init` shouild save xcodeproj if it was defined
Refactor repo spec to separate subcommands
[Repo remove] Improve test coverage
[Repo remove] Handle file permission errors

Fixes #1778
Include declared_path in 'No podspec found..' error message for PathSource (ref #1825)
Merge pull request #1832 from ericallam/issue-1825

Include declared_path in 'No podspec found..' error message for PathSource
validator.rb: Print xcodebuild command on -v.

Proposed in https://github.com/CocoaPods/Specs/pull/9179.
Merge pull request #1883 from modocache/print-xcodebuild-command

validator.rb: Print xcodebuild command on -v.