make Embed follow existing custom plugin structure

src/custom.zig

@@ -140,10 +140,10 @@ pub const Embed = struct {
     sndfile: *c.SNDFILE = undefined,
     buf: []f32 = undefined,
 
-    pub fn init(allocator: *std.mem.Allocator, filepath: []const u8) @This() {
+    pub fn init(allocator: *std.mem.Allocator, params: *plugins.ParmaMap) @This() {
         return Embed{
             .allocator = allocator,
-            .filepath = filepath,
+            .filepath = params.get("path").?,
         };
     }
 

src/lang.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 
 const plugin = @import("plugin.zig");
+const custom = @import("custom.zig");
 
 pub const ParseError = error{
     OutOfMemory,
@@ -188,13 +189,9 @@ pub const Command = struct {
         data: f32,
     });
 
-    pub const Embed = struct {
-        pub const base_tag = Tag.embed;
-        base: Command,
-        split: usize,
-        index: usize,
+    pub const Embed = CustomCommand(Tag.write, custom.Embed, struct {
         path: []const u8,
-    };
+    });
 
     pub const Rotate = struct {
         pub const base_tag = Tag.rotate;