- Added a stamina system
--- If a player is running, his/her stamina is slowly depleting. If it's zero, he/she can't run.
- New cvars:
--- fof_stamina_enabled | Enables the stamina system (used when running).
--- fof_stamina_depletion_speed | Changes the stamina depletion speed when running.
--- fof_stamina_regeneration_speed | Changes the stamina regeneration speed.