src/array.php: Add 'groupBy' function which will group the elements of an array (the second parameter, $orig) based on the "key" returned by the callable first parameter ($getKey); it's worth noting this is closer in functionality to the 'groupBy' method of Scala than the function by the same name in Haskell.
src/global-utils.php: Add 'head' here for global access.
src/webapp/base-framework.php: Phase-out concept of "HtmlPage", for interaction with controllers, in favor of a more simplified, generic, and customizable alternative whereby client code can simply inherit from a new "Renderable" class.