The runtime class field information.
See:
Properties
The documentation of the field. This information is only available 
if the compiler flag -D use_rtti_doc was in place. Otherwise, or 
if the field has no documentation, the value is null.
The line number where the field is defined. This information is only 
available if the field has an expression. 
Otherwise the value is null.
overloads:Null<List<ClassField>>
The list of available overloads for the fields or null if no overloads 
exists.