hero: allow different animation sequences for hero diagonal movements

[jorgegv]

Currently, diagonal movement of the hero is allowed, but horizontal animation sequences are used when moving diagonally. That is: RIGHT animation sequence when moving TR, R and LR; and LEFT animation sequence is used for TL, L and DL. UP and DOWN animation sequences are only used when moving strictly U and D, respectively.

Specific animation sequences should be allowed for TR, LR, TD, LD movement, and be used when moving in those directions. As a particular case, the current behaviour can be configured if we do not want to create so many animation sequences.

• Modify hero sprite data to add the 4 new animation sequences
• Modify hero movement to take into account the new 4 directions and anim sequences
• Modify GDATA and DATAGEN to allow specifying the new 4 anim sequences
• Modify DATAGEN.md document with new information
• Add hero config directive DIAGONAL_MOVE to allow (or not) diagonal movement, and conditionally compile it only if needed