Improve documentation of RPG_RT chunk types

[mateofio]

Once DBString and DBArray are used everywhere, refactor fields.csv to better document exactly what chunk types are used by RPG_RT. This will allow us to extend the type system for extensions and be more explicit about what is supported by RPG_RT.

We should be explicit about defining our own library of types in liblcf, and how they map directly to RPG_RT.

• Array<T,N> - RPG_RT uses fixed size arrays for some types. These do not have size fields. While we can and should continue to use DBArray, this allows for incompatible EasyRPG extensions such as bigger maps. If the RPG_RT type is encoded, we can detect and warn about compatibility at the liblcf layer.
• Vector - These use delphi dynamic arrays. They have size fields, but depending on the object the size counts bytes or "objects" such as 16 bit integers.
• Other designs TBD..