std.zon: better namespace for Serializer

Author: andrewrk

lib/std/zon.zig

@@ -38,6 +38,7 @@
 
 pub const parse = @import("zon/parse.zig");
 pub const stringify = @import("zon/stringify.zig");
+pub const Serializer = @import("zon/Serializer.zig");
 
 test {
     _ = parse;