xso-proc: add support for parsing attributes into Strings

This is bare-bones and is missing many features which we intend to add
in future commits, such as parsing from attributes whose names differ
from the field names and parsing into non-String types.

xso-proc/src/lib.rs

@@ -26,7 +26,10 @@ use quote::quote;
 use syn::*;
 
 mod compound;
+mod error_message;
+mod field;
 mod meta;
+mod scope;
 mod state;
 mod structs;
 mod types;