fix: re-export sp_core and sp_runtime (#853)

subxt/src/lib.rs

@@ -182,4 +182,8 @@ pub mod ext {
     pub use frame_metadata;
     pub use scale_bits;
     pub use scale_value;
+    #[cfg(feature = "substrate-compat")]
+    pub use sp_core;
+    #[cfg(feature = "substrate-compat")]
+    pub use sp_runtime;
 }