Create addRestoreCaseException function

[umairda]

I use the pluralize library frequently and wanted to be able to pluralize promo ID => promo IDs

I can add a plural rule but the restoreCase function restores the case so that the result is promo IDS

I created a function addRestoreCaseException which takes a token argument and pushes it to an array of restoreCaseExceptions

If a token is found in the array of restoreCaseExceptions then the token's case is not restored.

I also added a test and updated the readme.

[coveralls]

Coverage remained the same at 100.0% when pulling 184e7d0 on umairda:master into abb3991 on blakeembrey:master.