Import new Rust implementation (#143)

- break: This is a complete reimplementation in Rust of the old Haskell codebase. Although the full test suite passes, a few compromises have been made. Arbitrary precision arithmetic is no longer supported and a few undocumented dusty corners (IOSM) have been removed.
- perf: The new implementation is already faster for most use cases and has not been optimised as yet.

Author: gmorpheme

.changelog.yaml

@@ -0,0 +1,13 @@
+# Configuration for git-changelog
+
+conventions:
+  categories:
+    - {tag: "break", title: "Breaking Changes"}
+    - {tag: "feature", title: "Features"}
+    - {tag: "fix", title: "Fixes"}
+    - {tag: "perf", title: "Performance Improvements"}
+
+  scopes:
+    - {tag: "", title: ""}
+    - {tag: "api", title: "API"}
+    - {tag: "doc", title: "Documentation"}