Add documentation of data storage

doc_data.md

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+# Data Formats
+
+This file documents the contents of ctf.txt  
+Values are added to the file using ctf.register_on_save and ctf.register_on_load.  
+Here are the default values:
+
+```lua
+{
+	players = ctf.players,
+	teams = ctf.teams,
+	diplo = ctf.diplo.diplo
+}
+```
+
+## Players
+
+Commonly called tplayer (may be called data or player in old code).  
+Player name is commonly called name (but may be called other things in older code).
+
+```lua
+ctf.players = {
+	username = (player_table)
+}
+
+(player_table) = {
+	name = "username",
+	team = "teamname",
+	auth = false
+	-- true if the player is a team admin. Team admins can change team settings.
+	-- See ctf.can_mod()
+	-- Note that priv:ctf_admin can also change team settings
+}
+```
+
+## Teams
+
+Commonly called team.  
+Team name is commonly called tname (but may be called team in old code).
+
+```lua
+ctf.teams = {
+	teamname = (team_table)
+}
+
+(team_table) = {
+	data = {
+		name = "teamname",
+		color = "teamcolor" -- see ctf_colors
+	},
+	flags = {
+		(flag_table), (flag_table)
+	},
+	players = {
+		username1 = (player_table),
+		username2 = (player_table)
+	},
+	spawn = { x=0, y=0, z=0 }
+	-- fallback team spawn. Read by ctf.get_spawn() and overriding functions
+	-- Don't use directly, instead call ctf.get_spawn("teamname")
+}
+
+(flag_table) = {
+	x=0, y=0, z=0,
+	flag_name = "Capital" -- human readable name
+}
+```
+
+## Diplomacy
+
+```lua
+ctf.diplo.diplo = {
+	(diplo_table), (diplo_table)
+}
+
+(diplo_table) = {
+	one = "teamname1",
+	two = "teamname2",
+	state = "war" / "peace" / "alliance"
+}
+```