attempt to fix trailing whitespace, correct py3 to py

Author: AndrewAnnex

docs/how-to-guides/shared-libraries.rst

@@ -64,7 +64,7 @@ A shared library produced by ``library()`` or ``shared_library()`` built like th
 
 is installed to ``libdir`` by default. If the only reason the shared library exists
 is to be used inside the Python package being built, then it is best to modify
-the install location, via the ``install_dir`` argument, to be within 
+the install location, via the ``install_dir`` argument, to be within
 the Python package itself:
 
 .. code-block:: meson
@@ -73,15 +73,15 @@ the Python package itself:
         'example',
         'examplelib.c',
         install: true,
-        install_dir: py3.get_install_dir() / 'mypkg/subdir',
+        install_dir: py.get_install_dir() / 'mypkg/subdir',
     )
 
 Then an extension module in the same install directory can link against the
 shared library in a portable manner by using ``install_rpath``:
 
 .. code-block:: meson
 
-    py3.extension_module('_extmodule',
+    py.extension_module('_extmodule',
         '_extmodule.c',
         link_with: example_lib,
         install: true,