Make subxt-core ready for publishing (#1508)

* Move Extrinsic decoding things to subxt_core and various tidy-ups

* A couple more fixes and fmt

* first pass moving tx logic to subxt_core

* cargo fmt

* fix wasm example

* clippy

* more clippy

* WIP Adding examples and such

* Move storage functionality more fully to subxt_core and nice examples for storage and txs

* Add example for events

* consistify how addresses/payloads are exposed in subxt-core and add runtime API fns

* Add runtime API core example

* fmt

* remove scale-info patch

* Add a little to the top level docs

* swap args around

* clippy

* cargo fmt and fix wasm-example

* doc fixes

* no-std-ise new subxt-core additions

* alloc, not core

* more no-std fixes

* A couple more fixes

* Add back extrinsic decode test

codegen/src/lib.rs

@@ -224,7 +224,16 @@ impl CodegenBuilder {
     }
 
     /// Set the path to the `subxt` crate. By default, we expect it to be at `::subxt::ext::subxt_core`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the path provided is not an absolute path.
     pub fn set_subxt_crate_path(&mut self, crate_path: syn::Path) {
+        if absolute_path(crate_path.clone()).is_err() {
+            // Throw an error here, because otherwise we end up with a harder to comprehend error when
+            // substitute types don't begin with an absolute path.
+            panic!("The provided crate path must be an absolute path, ie prefixed with '::' or 'crate'");
+        }
         self.crate_path = crate_path;
     }