Attempt to register metadata.

Haxe will display the documentation if you call `haxe --library echoes --help-user-metas` from the command line, but vshaxe still doesn't pick it up.

extraParams.hxml

@@ -1 +1,2 @@
---macro echoes.macro.ComponentStorageBuilder.invalidate()
+--macro echoes.macro.ComponentStorageBuilder.invalidate()
+--macro echoes.macro.MacroTools.registerDescriptionFiles()

meta.json

@@ -0,0 +1,77 @@
+[
+	{
+		"metadata": ":add",
+		"doc": "Makes a system function handle add events. The function will be called once an entity has the required components.",
+		"targets": ["TClassField"],
+		"links": ["./README.md#usage"]
+	},
+	{
+		"metadata": ":echoes_add",
+		"doc": "Disambiguation alias for @:add.",
+		"targets": ["TClassField"],
+		"links": ["./README.md#usage"]
+	},
+	{
+		"metadata": ":update",
+		"doc": "Makes a system function handle updates. Each update, it will be called for every entity that has the required components.",
+		"targets": ["TClassField"],
+		"links": ["./README.md#usage"]
+	},
+	{
+		"metadata": ":echoes_update",
+		"doc": "Disambiguation alias for @:update.",
+		"targets": ["TClassField"],
+		"links": ["./README.md#usage"]
+	},
+	{
+		"metadata": ":remove",
+		"doc": "Makes a system function handle remove events. The function will be called when an entity loses one of the required components, if it previously had all of them.",
+		"targets": ["TClassField"],
+		"links": ["./README.md#usage"]
+	},
+	{
+		"metadata": ":echoes_remove",
+		"doc": "Disambiguation alias for @:remove.",
+		"targets": ["TClassField"],
+		"links": ["./README.md#usage"]
+	},
+	{
+		"metadata": ":echoes_replace",
+		"doc": "Marks a type so that when added to an entity, if it already had a component of that type, a remove event will be dispatched first.",
+		"targets": ["TAbstract", "TClass", "TEnum", "TTypedef"]
+	},
+	{
+		"metadata": ":priority",
+		"doc": "Sets the priority of a system or system function. Higher priorities happen first, and negative priorities are possible. The default priority is 0.",
+		"params": ["Integer"],
+		"targets": ["TClass", "TClassField"],
+		"links": ["./README.md#priority"]
+	},
+	{
+		"metadata": ":echoes_priority",
+		"doc": "Disambiguation alias for @:priority.",
+		"params": ["Integer"],
+		"targets": ["TClass", "TClassField"],
+		"links": ["./README.md#priority"]
+	},
+	{
+		"metadata": ":arguments",
+		"doc": "One or more component types to be taken as arguments in the entity template's constructor. Requires @:build(echoes.Entity.build()).",
+		"params": ["Type or type check"],
+		"targets": ["TAbstract"],
+		"links": ["./README.md#entity-templates", "./README.md#type-check-syntax"]
+	},
+	{
+		"metadata": ":optionalArguments",
+		"doc": "One or more component types to be taken as optional arguments in the entity template's constructor. Requires @:build(echoes.Entity.build()).",
+		"params": ["Type or type check"],
+		"targets": ["TAbstract"],
+		"links": ["./README.md#entity-templates", "./README.md#type-check-syntax"]
+	},
+	{
+		"metadata": ":echoes_storage",
+		"doc": "Sets the ComponentStorage instance used to store components of this type.",
+		"params": ["Constructor call or singleton instance"],
+		"targets": ["TAbstract", "TClass", "TEnum", "TTypedef"]
+	}
+]

src/echoes/macro/MacroTools.hx

@@ -3,6 +3,7 @@ package echoes.macro;
 #if macro
 
 import haxe.Exception;
+import haxe.macro.Compiler;
 import haxe.macro.Expr;
 import haxe.macro.Printer;
 import haxe.macro.Type;
@@ -213,6 +214,16 @@ class MacroTools {
 		}
 	}
 
+	public static function registerDescriptionFiles():Void {
+		var path:String = ((?infos:haxe.PosInfos) -> infos.fileName)();
+		if(!StringTools.endsWith(path, "src/echoes/macro/MacroTools.hx")) {
+			throw "MacroTools.hx moved, please update its path.";
+		}
+		path = path.substring(0, path.length - "src/echoes/macro/MacroTools.hx".length);
+
+		Compiler.registerMetadataDescriptionFile(path + "meta.json", "echoes");
+	}
+
 	/**
 	 * Gets the underlying `BaseType`, if available.
 	 */