[Documentation] Fix example hashbang alignment
[Specification] Raise an Informative error if there is a case mis-match in #subspec_by_name

Closes https://github.com/CocoaPods/Core/issues/185
[Specification::JSON] Add #to_pretty_json method
[Specification::JSON] Add specs for #to_pretty_json
[Specification] Evaluate a Specification in .from_string in the context of the path parameter
[Documentation] Fix spacing
[Changelog] Add entry for spec eval context