Define WREN_VERSION_MAJOR, WREN_VERSION_MINOR, WREN_VERSION_PATCH macros,
WREN_VERSION_STRING "0.1.0", and WREN_VERSION_NUMBER for monotonic checks.
Update REPL banner to use WREN_VERSION_STRING instead of hardcoded "v0.0.0".
Create CHANGELOG.md documenting the first declared version.
