parser: Add a forgotten exception
Introduce 'Tile' as a class, prepare for map layers

Tile as a class is easier to modify with inheritance.  Since map layers
can define new tiles, this inheritance will be usefull to extends
existing tiles.

Also, this reworks is needed for futur work on generic tile parsing.
Merge branch 'master' of https://github.com/Jeremagician/MiniLD53