feat: add versioning infrastructure and bump to 0.1.0

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.

src/cli/vm.c

@@ -257,7 +257,7 @@ int runRepl()
   initVM();
 
   printf("\\\\/\"-\n");
-  printf(" \\_/   wren v0.0.0\n");
+  printf(" \\_/   wren v%s\n", WREN_VERSION_STRING);
 
   char line[MAX_LINE_LENGTH];