FGD (Forge Game Data) is a configuration format used by the Hammer editor to define the entities available in the editor and their properties.
This module is based on my previous vmfparser, and exposes a similar API.
It exports a single parse(input, options) function, with the input being
an FGD source string, and options is an optional object with the following
properties:
ast: If true, will return the Abstract Syntax Tree instead of the transformed object.