[pod] Whitelist pods for configurations

An option to only link a specific pod to the target when building in a specific configuration.
The exact syntax is still TBD, pending discussion in https://github.com/CocoaPods/CocoaPods/pull/1668
which implements the corresponding functionality.
[pod] whitelisting: code style and specs
[pod] Whitelist pods for configurations

An option to only link a specific pod to the target when building in a specific configuration.
The exact syntax is still TBD, pending discussion in https://github.com/CocoaPods/CocoaPods/pull/1668
which implements the corresponding functionality.
[pod] whitelisting: code style and specs
[TargetDefinition] Coerce configuration names from user input to strings.
[TargetDefinition] Return list of all configurations for which pods have been whitelisted.
[TargetDefinition] Make predicate method more Ruby-ish.
[TargetDefinition] Also take singular :configuration for whitelisting.
[TargetDefinition] Cleanup docs.
A spec is not longer empty if it contains a resource_bundle

Closes #63
Frameworks should not allow non-alphanumeric characters
Libraries should not allow non-alphanumeric characters
Merge pull request #95 from CocoaPods/resource_bundle_not_empty

A spec is not longer empty if it contains a resource_bundle
Improved linter comments
Extracted regex to a variable
Updated changelog
ignore any entry that begins with a period
Merge branch 'master' of https://github.com/squarefrog/Core into squarefrog-master

* 'master' of https://github.com/squarefrog/Core:
  Updated changelog
  Extracted regex to a variable
  Improved linter comments
  Libraries should not allow non-alphanumeric characters
  Frameworks should not allow non-alphanumeric characters

Conflicts:
	CHANGELOG.md
[Changelog] Wording
[Rubocopo] Be happy!