Fix native_libs.txt (#16)

When building additional, auxiliary libraries they should receive
proper handling in "native_libs.txt". Surprisingly, this only
happens when a trailing `/` is added.

Also, the primary module will then go into the package directory.

Additional `RPATH`/`RUNPATH` handling for auxiliary, "native" libs
is likely needed. E.g. on Linux/OSX:

```
            '-DCMAKE_INSTALL_RPATH=$ORIGIN',
            '-DCMAKE_BUILD_WITH_INSTALL_RPATH:BOOL=ON',
            '-DCMAKE_INSTALL_RPATH_USE_LINK_PATH:BOOL=OFF',
```

while on Windows one can just keep a flat structure in the package,
which will be in `%PATH%`.

Author: ax3l

setup.py

@@ -33,6 +33,10 @@ def run(self):
 
     def build_extension(self, ext):
         extdir = os.path.abspath(os.path.dirname(self.get_ext_fullpath(ext.name)))
+        # required for auto-detection of auxiliary "native" libs
+        if not extdir.endswith(os.path.sep):
+            extdir += os.path.sep
+
         cmake_args = ['-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=' + extdir,
                       '-DPYTHON_EXECUTABLE=' + sys.executable]