Fix configs, update docs, resolve discovered regressions

docs/modders/Entities_Format/Bonus_Types_Format.md

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+# Battlefield Format
+
+WARNING: currently custom bonus types can only be used for custom "traits", for example to use them in limiters. At the moment it is not possible to provide custom mechanics for such bonus
+
+```json
+{
+	// If set to true, this bonus will be hidden in creature view
+	"hidden" : false,
+
+	// If set to true, this bonus will be considered a "creature nature" bonus
+	// If creature has no creature nature bonuses, it is considered to be a LIVING creature
+	"creatureNature" : false,
+	
+	// Generic human-readable description of this bonus
+	// Visible in creature window
+	// Can be overriden in creature abilities or artifact bonuses
+	"description" : "{Bonus Name}\nBonus description",
+	
+	"graphics" : {
+		// Generic icon of this bonus
+		// Visible in creature window
+		// Can be overriden in creature abilities or artifact bonuses
+		"icon" : "path/to/icon.png",
+		
+		// Custom icons for specific subtypes of this bonus
+		"subtypeIcons" : {
+			"spellSchool.air" : "",
+			"spellSchool.water" : "",
+		},
+		
+		// Custom icons for specific values of this bonus
+		// Note that values must be strings and wrapped in quotes
+		"valueIcons" : {
+			"1" : "",
+			"2" : "",
+		}
+	},
+	
+	// Custom descriptions for specific subtypes of this bonus
+	"subtypeDescriptions" : {
+		"spellSchool.air" : ""
+		"spellSchool.water" : "",
+	},
+	
+	// Custom descriptions for specific values of this bonus
+	// Note that values must be strings and wrapped in quotes
+	"valueDescriptions" : {
+			"1" : ""
+			"2" : ""
+		}
+	}
+}
+```

docs/modders/Entities_Format/Spell_School_Format.md

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+# Spell School Format
+
+WARNING: currently custom spell schools are only partially supported:
+
+- it is possible to use custom spell schools in bonus system
+- it is possible to make skill for specializing in such spell
+- it is possible to specify border decorations for mastery level of such spell in spellbook
+- it is NOT possible to add "bookmark" filter for spellbook for spells of such school
+
+```json
+	// Internal field for H3 schools. Do not use for mods
+	"index" : "",
+	
+	// animation file with spell borders for spell mastery levels
+	"schoolBorders" : "SplevA"
+```