Improve the disassembly of map headers

For now map headers data is not separated from the map blocks.

It looks like this:

Overworld00::
  db   $0B, $E5, $8A, $00, $00, $8A, $10, $00, $8A, $20, $EF, $10, $7C, $11, $7D, $19, $7C, $13, $80, $84, $14, $4D, $17, $81, $23, $37, $83, $24, $0A, $27, $38, $32, $1D, $33, $2E, $34, $48, $36, $49, $37, $4E, $38, $5D, $41, $1D, $42, $37, $43, $39, $44, $E1, $E1, $07, $3A, $58, $10, $82, $45, $3A, $C2, $35, $E0, $47, $3B, $48, $38, $50, $1D, $C3, $51, $37, $C2, $52, $37, $85, $53, $09, $82, $58, $7A, $C2, $60, $37, $85, $63, $09, $68, $38, $72, $2E, $85, $73, $2F, $78, $4E, $69, $50, $79, $09, $FE

This should be improved, by:

• Documenting the header structure (in tools/generate_map_data.py) ;
• Maybe moving the blocks to separate files (like data/blocks/overworld_00.blk).

It could look like this:

Overworld00::
  db ANIMATION_TARAMANCH ; animated tiles set
  db WALLS_NONE | FLOOR_MOUNTAINS ; walls and floor type
  incbin 'data/blocks/overworld_00.blk'

All this data is already parsed by tools/generate_map_data.py. It should just be a matter of augmenting the script to output the right informations.