Add the ability to directly set version parts.

- Move unittests to a dedicated file.
- Rework CLI making version part selection an option that can be passed
  into many commands.
- Add support for updates to version constants defined in soruce files.

.gitea/workflows/pr-validation.yaml

@@ -26,9 +26,9 @@ jobs:
       - name: Build unittests
         run: |
           printf "🔨\033[0;32m Compiling unit tests...\033[0m\n" >&1
-          nimble build
+          nimble c tupdate_version.nim
 
       - name: Run unittests
         run: |
           printf "🧪\033[0;32m Running unit tests...\033[0m\n" >&1
-          ./update_version test
+          ./tupdate_version