parse constructors
use Control.Lens
use Lens to generalize most of the parsers
parse variables
parse fields
fix base parsing
fix parseArgument using Ellipsis and filterElems
arguments don't always have FileID
parse typedefs
parse reference types
parse pointer types
parse MethodType and CvQualifiedType
parse FunctionType
parse unions
parse offset type
Context is a newtype, not an Id now
parse destructors
make Returns a newtype
parse Converter
parse OperatorFunction