Support no-nesting via NONEST conditional

[atifaziz]

According to @albahari in a post to a thread in the LINQPad Forum:

Normally, anything types that you define end up as nested types, because LINQPad wraps everything that you enter into a class definition. You can tell LINQPad to extract the classes and define them as non-nested by adding the following to the beginning of your query:

#define NONEST

Add support for the same to this project.