Implement DeprecatedVariable for deprecating module level variables

[radeklat]

• Add class DeprecatedVariable

• Abstract warning check into _get_warning_class()
• Abstract warning raising into _warn_user()
• Abstract docstring wrapping into _wrap_doctring()

• Implement tests for DeprecatedVariable

• Update README to mention DeprecatedVariable

[codecov-io]

Codecov Report

Merging #35 into master will not change coverage. The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #35   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          83    110   +27     
  Branches       16     20    +4     
=====================================
+ Hits           83    110   +27

Impacted Files	Coverage Δ
deprecation.py	100% <100%> (ø)	:arrow_up:

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[briancurtin]

Cool! Thanks for writing this up! I have a few things to think about and will try to get you a review for this in the next few days.

[Julian]

Don't think this is the right approach personally, but Twisted, which is the best implementor of this functionality that I'm aware of, is as usual a decent place to use as a cheat sheet for this functionality IMHO.