add CustomCommand function

src/lang.zig

@@ -31,6 +31,23 @@ fn LV2Command(
     };
 }
 
+fn CustomCommand(
+    comptime tag: Command.tag,
+    comptime plugin: type,
+    comptime parameters: type,
+) type {
+    return struct {
+        pub const base_tag = tag;
+        pub const command_type = CommandType.plugin_command;
+        pub const plugin_type = plugin;
+
+        base: Command,
+        split: usize,
+        index: usize,
+        parameters: LV2Parameters,
+    };
+}
+
 pub const Command = struct {
     tag: Tag,
 
@@ -182,7 +199,7 @@ pub const Command = struct {
     pub const Rotate = struct {
         pub const base_tag = Tag.rotate;
         base: Command,
-        deg: usize,
+        deg: f32,
         bgfill: []const u8,
     };