Tileset Builder:

    [ ] Finish consolidating tilesets into AtlasBuilder
------->[ ] While tilesets have their own "Builder", Anims, Fonts and Maps should be saved directly in the Renderer to ensure a single entry for each corresponding Enum variant.

    [x] Save and Load Group data

        Save all group enum variants with their respective data, or...
        Save only the groups explicitly inserted into tileset?

    [x] Save and Load Anim data

    [x] Save and Load Tilemap data

    [x] Anim consts should be unique (per Renderer), but groups shouldn't (no tileset stored, works in any tileset/tilemap).
        - Anims are about looks, which tiles to use
        - Groups are about functionality, no need to restrict to a tile
        - That means a "Font" should be its own thing: a range of tiles within a tileset, neither Anim or Group

    [/] Use keychains instead of Enums?
        Pros:
            - Direct access to/from u8
            - Group count is defined in build script
        Cons:
            - Naming mechanism? Runtime init now has difficulty assigning index to a variable. I.e. which   index is "IdleAnim"?
        Ideas:
            [/] Instead of KeyChains, simply use named constants in globals.rs, like this:
                pub const SPY_IDLE:u8 = 0;
                pub const SPY_RUN:u8 = 1;
            [/] Still use Enums, but only as a way to obtain the u8 indices, NOT as generic params!
                - All members/arguments would be u8, never an enum type.
                - That way "try_from" casts are unnecessary, and so are excessive generic enums in structs.
                - implementing "Into<u8>" may be useful to allow functions to take an unknown type (i.e. our enums) as long as it converts to u8.
                - Dropped. Too much friction/unnecessary complexity for little benefit.
            [x] Using u8 numbers as group info for now.

    [x] Palettes!
        [x] Remove hard coded palette size (search for "TODO" items to find all)
        [ ] Per asset (Sprite, Tilemap) palette? Maybe per Tile palette?