Compile wrapper.pyx under the name libzim.

Instead of creating a submodule named `libzim.wrapper`,
let's directly create a libzim module.

This break tests as we cannot import submodules anymore but it will
be fixed in next commits.

Author: mgautierfr

libzim/__init__.py

@@ -34,7 +34,7 @@
 ObjWrapper::ObjWrapper(PyObject* obj)
   : m_obj(obj)
 {
-  if (import_libzim__wrapper()) {
+  if (import_libzim()) {
     std::cerr << "Error executing import_libzim!\n";
     throw std::runtime_error("Error executing import_libzim");
   }

libzim/libwrapper.cpp

@@ -18,7 +18,7 @@
 # along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 
-cimport libzim.zim as zim
+cimport zim
 
 import os
 import enum

libzim/wrapper.pyx

@@ -87,7 +87,7 @@ def get_long_description():
 
 
 wrapper_extension = Extension(
-    name="libzim.wrapper",
+    name="libzim",
     sources=["libzim/wrapper.pyx", "libzim/libwrapper.cpp"],
     include_dirs=["libzim", LIBZIM_INCLUDE_DIR],
     libraries=["zim"],