better support of PACKAGE_DST environment variable

setup.py

@@ -1,11 +1,17 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
-from setuptools import setup, find_packages
+from setuptools import setup
 import os
 from tiramisu import __version__
 
 
-PACKAGE_NAME = os.environ.get('PACKAGE_DST', 'tiramisu')
+ORI_PACKAGE_NAME = 'tiramisu'
+PACKAGE_NAME = os.environ.get('PACKAGE_DST', ORI_PACKAGE_NAME)
+
+if PACKAGE_NAME != ORI_PACKAGE_NAME:
+    package_dir = {PACKAGE_NAME: ORI_PACKAGE_NAME}
+else:
+    package_dir = None
 
 setup(
     version=__version__,
@@ -40,5 +46,6 @@ producing flexible and fast options access.
 This version requires Python 3.5 or later.
 """,
     include_package_data=True,
-    packages=find_packages(include=['tiramisu'])
+    package_dir=package_dir,
+    packages=[PACKAGE_NAME],
 )