Add a setup.py command for cleaning built code.

setup.py

@@ -1,5 +1,6 @@
 import os
-from setuptools import setup
+import shutil
+from setuptools import Command, setup
 
 
 def extensions():
@@ -92,6 +93,28 @@ def extensions():
     ]
 
 
+class CleanExtCommand(Command):
+    description = 'Clean all compiled python extensions from the current directory.'
+
+    user_options = []
+
+    def initialize_options(self) -> None:
+        pass
+
+    def finalize_options(self) -> None:
+        pass
+
+    def run(self) -> None:
+        print("Removing build directory...")
+        shutil.rmtree(os.path.abspath("build/"), ignore_errors=True)
+        for dirname, subdirList, fileList in os.walk(os.path.abspath("bemani/")):
+            for filename in fileList:
+                if filename[-3:] == ".so":
+                    fullname = os.path.join(dirname, filename)
+                    print(f"Removing {fullname}")
+                    os.remove(fullname)
+
+
 setup(
     name='bemani',
     version='1.0',
@@ -170,6 +193,9 @@ setup(
     # remove the ext_modules line and run setuptools again. Everything should work, but
     # it will run slower.
     ext_modules=extensions(),
+    cmdclass={
+        'clean_ext': CleanExtCommand,
+    },
     include_package_data=True,
     zip_safe=False,
 )