Implemented the functional list in PHP.
Reimplement `Map` in C# using polymorphism.
Reimplement `map` in Java using polymorphism.
Reimplement `map` in JavaScript using polymorphism.
Reimplement `map` in Python using polymorphism.
Make `fromArray` a part of the Python FunctionalList class, because inner methods suck.
Stop taking slices of arrays in PHP when constructing a FunctionalList.
Move the PHP function `list_of` to `FunctionaList::of`.
Reimplement `map` in Ruby using polymorphism.
In PHP, move `nil` and `cons` inside the class.