config: Refactor Map to its own file + Better errors.

- Don't use log.Fatalf in ParseFile method, return error.
proto/packet: Refactor chunk packets 0x33 & 0x38.

Both:
- Renamed field GroundUpContinuous -> AllColSections.
MapChunkBulk
- Deleted Count and Length fields in favor of slices len builtin
function.