Fix handling of default proc values in Mash
Merge pull request #259 from Erol/fix-default-array-values

Fix handling of default proc values in Mash
Add block to Extensions::DeepMerge
Merge pull request #260 from Galathius/add-block-to-deep-merge-extension

Add block to Extensions::DeepMerge
Public utility methods for stringify/symbolize keys
Corrected typo.
Upgraded RuboCop to 0.28.0.
Minor language updates.
Made a 1-liner shorter.