Changelog: Add a changelog file listing the releases

Including the prospective 1.0.1

CHANGELOG.md

+# Release Documentation - changelog
+
+## Changelog
+
+### 1.0.1
+
+ * Two minor docs fixes.
+
+### 1.0.0
+
+ * Minor docs improvements.
+ * Declare it stable.
+
+### 0.1.0
+
+ * Check for allocator failures (soundness fix).
+ * Significantly rework the implementation.
+ * Significantly extend the APIs.
+ * CI tests including miri tests.
+
+### 0.0.1
+
+ * Preview release only.
+ * Initial import of code from an inner module in arti.git.