Correct implementation of pkgutil style namespace (Fixes #144) (#145)

* Fix for #144

Change to correct use of pkgutil style namespace packages as documented https://packaging.python.org/guides/packaging-namespace-packages/#pkgutil-style-namespace-packages and illustrated in https://github.com/pypa/sample-namespace-packages/tree/master/pkgutil

Note: at the moment the `namespace_packages` directive is completely ignored, if you add the "luma" package to `packages` (in addition to `namespace_packages`) then `setup.py build` returns an error because it is expecting a pkg_resources style namespace package:

```
running build
running build_py
error: Namespace package problem: luma is a namespace package, but its
__init__.py does not call declare_namespace()! Please fix it.
(See the setuptools manual under "Namespace Packages" for details.)
```

Note: in the linked example the `find_packages()` method returns the "namespace" package as if it were an ordinary package.

* Update CONTRIBUTING.rst

CONTRIBUTING.rst

@@ -29,3 +29,4 @@ Contributors
 * Jonathan Pereira (@jonathanrjpereira)
 * Daniel Smullen (@drspangle)
 * Hans Liss (@hansliss)
+* Phil Howard (@gadgetoid)

setup.py

@@ -51,8 +51,7 @@ def find_version(*file_paths):
     keywords="raspberry orange banana pi rpi opi sbc oled lcd led display screen spi i2c",
     url="https://github.com/rm-hull/luma.core",
     download_url="https://github.com/rm-hull/luma.core/tarball/" + version,
-    namespace_packages=["luma"],
-    packages=["luma.core", "luma.core.legacy", "luma.core.interface"],
+    packages=["luma", "luma.core", "luma.core.legacy", "luma.core.interface"],
     install_requires=install_deps,
     setup_requires=pytest_runner,
     tests_require=test_deps,