Added do while loop
If statements can now provide only the truth evaluation

Previously an if statement required both a true and false evaluation.
Now only the true eval is needed. If this kind of statement evaluates
as false, an empty q-expression (nil) is returned.
Separated standard library into a core library and the new standard lib

The core library is loaded with the interpreter. Core functions such
as loops, boolean values, list manipulations, and function declarations
are by default available to scripts. The standard library will contain
only functions whose purposes are not necassarily vital to the core
language.