Don't ship pam.py in the module

The comment at the top of this file says:
"This is a legacy file, it is not used. Here for example."
so it seems sensible to no longer ship it as part of the pam
module itself. This moves it to an examples/ directory which
will not be included in builds of the actual module, and updates
the comment.

Signed-off-by: Adam Williamson <[email protected]>

Author: AdamWill

MANIFEST.in

@@ -1,2 +1,3 @@
 include README.md
 include LICENSE
+graft examples

src/pam/pam.py renamed to examples/pam.py

@@ -22,15 +22,16 @@
 '''
 PAM module for python
 
-This is a legacy file, it is not used. Here for example.
+This is a legacy implementation of the real module, kept around as a usage
+example.
 
 Provides an authenticate function that will allow the caller to authenticate
 a user against the Pluggable Authentication Modules (PAM) on the system.
 
 Implemented using ctypes, so no compilation is necessary.
 '''
 
-import __internals
+import pam.__internals
 
 if __name__ == "__main__":  # pragma: no cover
     import readline