refactor: update to proc_macro_error2 (#661)

Author: molpopgen

Diff for: Cargo.lock

@@ -14,4 +14,4 @@ proc-macro = true
 [dependencies]
 syn = { version = "1.0", features = ["derive"] }
 quote = "1.0"
-proc-macro-error = "1.0.4"
+proc-macro-error2 = "2.0"

Diff for: tskit-derive/Cargo.toml

@@ -64,25 +64,25 @@ fn impl_metadata_roundtrip_macro(ast: &syn::DeriveInput) -> Result<TokenStream,
             } else if &serializer == "bincode" {
                 return Ok(impl_serde_bincode_roundtrip(name));
             } else {
-                proc_macro_error::abort!(serializer, "is not a supported protocol.");
+                proc_macro_error2::abort!(serializer, "is not a supported protocol.");
             }
         } else {
-            proc_macro_error::abort!(attr.path, "is not a supported attribute.");
+            proc_macro_error2::abort!(attr.path, "is not a supported attribute.");
         }
     }
 
-    proc_macro_error::abort_call_site!("missing [serializer(...)] attribute")
+    proc_macro_error2::abort_call_site!("missing [serializer(...)] attribute")
 }
 
 macro_rules! make_derive_metadata_tag {
     ($function: ident, $metadatatag: ident) => {
-        #[proc_macro_error::proc_macro_error]
+        #[proc_macro_error2::proc_macro_error]
         #[proc_macro_derive($metadatatag, attributes(serializer))]
         /// Register a type as metadata.
         pub fn $function(input: TokenStream) -> TokenStream {
             let ast: syn::DeriveInput = match syn::parse(input) {
                 Ok(ast) => ast,
-                Err(err) => proc_macro_error::abort!(err),
+                Err(err) => proc_macro_error2::abort_call_site!(err),
             };
             let mut roundtrip = impl_metadata_roundtrip_macro(&ast).unwrap();
             let name = &ast.ident;