Implement package version retrieval

Add versioning information to the package.

Author: ss0832

multioptpy/__init__.py

@@ -1,5 +1,13 @@
+from importlib.metadata import version, PackageNotFoundError
+
+try:
+    __version__ = version("MultiOptPy")
+except PackageNotFoundError:
+    __version__ = "unknown"
+
 from . import interface
 from . import neb
 from . import ieip
 from . import moleculardynamics
 from . import optimization
+