Adds decorator to deprecate functions and methods

The deprecated decorator logs a deprecation message when the callable it
decorates is used. The message will include the release where the callable
was deprecated, the release where is may be removed and possibly an
optional replacement.

Change-Id: Ic6260ce9d8950afa248c0f7842817e7312a4d5a7
Merge "Adds decorator to deprecate functions and methods"
Fix some doc string nits in crypto/utils.py

These were noticed when importing the module into Heat.

Change-Id: I5a5b7581ad92bc0710f2d518ce371c2b73fca7f9