Added "ThenSomething" and "ThenMaybeSomething" methods
Introduced QuantifiedSubexpression base class
Escaping a literal string now happens within the "Literal" class
Use a LinkedList instead of a regular List to store the subexpressions
Added overloads excepting a Subexpression for the different lookaround methods. Also, the FriendlyRegex class is now terser
Added verification that grouping parentheses are placed correctly