Improvements to deprecated

[pberkes]

• Raises a DeprecationWarning
• Function to clear up the global cache

[coveralls]

Coverage decreased (-0.44%) when pulling 3afc043 on feature/improve-deprecated into 83eb368 on master.

[coveralls]

Coverage increased (+0.08%) when pulling e190014 on feature/improve-deprecated into 83eb368 on master.

[pberkes]

Ready for review.

[mdickinson]

PEP 8 violation (long line)

[coveralls]

Coverage decreased (-0.1%) when pulling 5e7192a on feature/improve-deprecated into a1f8b32 on master.

[mdickinson]

This is a more drastic change, but how about we simply issue the DeprecationWarning and remove the logged warning and all the caching machinery?

[pberkes]

@mdickinson I'm not sure if the logs are a wanted feature or not. Myself, I won't miss them

[mdickinson]

Looking at this again, we should definitely remove the caching machinery: as a library, Traits should simply emit the warning and/or log message unconditionally. If an application using Traits only wants to see the first occurrence of a particular warning or log message, then that application should configure warnings or logging appropriately.

That leaves the question of whether we should be issuing logs or warnings or both for deprecated machinery: I think we should just issue the warnings. That's the standard Python way to warn about deprecations.

[mdickinson]

See #220 for an alternative proposal.

[mdickinson]

Closing this in favour of #220, which has now been merged.