Added --relative-only option to bat pack command

This makes BAT skip assets that are referred to with an absolute path.
It is assumed that the receiver of the BAT pack can access those assets
at the same path.

blender_asset_tracer/pack/__init__.py

@@ -99,12 +99,14 @@ class Packer:
                  target: pathlib.Path,
                  *,
                  noop=False,
-                 compress=False) -> None:
+                 compress=False,
+                 relative_only=False) -> None:
         self.blendfile = bfile
         self.project = project
         self.target = target
         self.noop = noop
         self.compress = compress
+        self.relative_only = relative_only
         self._aborted = threading.Event()
         self._abort_lock = threading.RLock()
 
@@ -233,6 +235,10 @@ class Packer:
                 log.info('Excluding file: %s', asset_path)
                 continue
 
+            if self.relative_only and not usage.asset_path.startswith(b'//'):
+                log.info('Skipping absolute path: %s', usage.asset_path)
+                continue
+
             if usage.is_sequence:
                 self._visit_sequence(asset_path, usage)
             else: