Adjust player_t struct, stats narration, etc.

Adjusted character stat constants, made further changes to the player_t
struct and various functions that interact with it, and overhauled the
stats narration (which now has four parts with better formatting). Also
adjusted leveling criteria and added max. level enforcement in
"damage_npc", added max. depth enforcement in "init_location", and added
the "get_player_max_health" and "get_player_max_energy" functions as an
experiment.