added functionality for various game modes

GameModes/nostaminaregen.tres

@@ -0,0 +1,34 @@
+[gd_resource type="Resource" script_class="gamemode" load_steps=2 format=3 uid="uid://65tl6q463gxl"]
+
+[ext_resource type="Script" path="res://gamemode.gd" id="1_d71ib"]
+
+[resource]
+script = ExtResource("1_d71ib")
+win_conditions = 0
+gamemode_name = "no stamina regen, no health drops"
+survival_time = 160.0
+walk_speed = 12.0
+jump_velocity = 5
+dash_speed = 40
+gravity = -9.8
+time_slowed_speed = 0.1
+stamina_regen = false
+max_stamina = 100.0
+stamina_drain = 5.0
+air_dash_max = 1
+load_save = false
+money = 10
+start_health = 10
+drop_chance_minimum = 0.1
+random_drops = false
+ammo_drop_enabled = true
+expected_ammo = {
+"heavy": 25,
+"light": 200,
+"medium": 50,
+"rocket": 3,
+"shotgun": 20
+}
+stamina_drop_enabled = true
+health_drop_enabled = true
+money_drop_enabled = true