Add recipes to install an array of formulas/casks

This operates similar to Matt Ray's "packages" cookbook. A list of formulas can be created as an array, and the `install_formulas` recipe will iterate over it and install each formula as a brew package. Similarly, a list of casks can be specified and installed using the `install_casks` recipe. 

I used "formulas" instead of "formulae" as this pertains to "a list of ingredients for or constituents of something", rather than of a mathematical relationship, to use the OS X Dictionary.app's definition. As this is for an OS X-related cookbook, I thought it appropos to use such definition, as words matter.