[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.
Updated yaml_helper_spec and yaml_helper to detect merge conflicts with the supplied YAML. Also made distinction on YAMLHelper methods.. i.e. string v file
clean up from previous test adjustments
updated remaining specs, corrected necessary code to accomodate new #load_string and #load_file methods on YAMLHelper
removed pry require
changed #load_file to only accept/enforce Pathname as param
changed docs to reflect method changes, improved docs on earlier method change too
took care of the hound and robocop
added changelog annotation
some white space
Merge branch 'pods-by-config' of github.com:lookback/Core into lookback-pods-by-config

* 'pods-by-config' of github.com:lookback/Core:
  [pod] whitelisting: code style and specs
  [pod] Whitelist pods for configurations

Conflicts:
	lib/cocoapods-core/podfile/target_definition.rb
	spec/podfile/target_definition_spec.rb
Style: adjustements