Update the versions in the sub-crate READMEs as well

sigma-compiler-core/README.md

@@ -1,5 +1,5 @@
 `sigma-compiler-core` by Ian Goldberg, iang@uwaterloo.ca  
-Version 0.1.0, 2025-10-10
+Version 0.2.1, 2026-03-26
 
 This crate provides the core functionality for the macros in the
 [`sigma-compiler`](https://crates.io/crates/sigma-compiler) crate.

sigma-compiler-derive/README.md

@@ -1,5 +1,5 @@
 `sigma-compiler-derive` by Ian Goldberg, iang@uwaterloo.ca  
-Version 0.1.0, 2025-10-10
+Version 0.2.1, 2026-03-26
 
 This crate provides the derive macros for the
 [`sigma-compiler`](https://crates.io/crates/sigma-compiler) crate.