[geracosta]

docs for two parser changes:

• tower_damage_t, added in Add tower_damage_t parser#98: per-minute tower damage from the game's own counter, empty for replays that don't have it
• hero_damage_t, moved to the game's hero damage counter in Take hero_damage_t from the game's counter parser#99. the current description says the final value matches hero_damage up to the last minute boundary, which only held for 204 of 250 players with the combat log sum; with the counter it does

no schema change: both live in the parsed blob.