stacklevel 2 warnings

[wimglenn]

Use stacklevel=2 for deprecation warnings, so the source/line number of user code is indicated, instead of the source/line of the library itself.

$ cat user_code.py 
# in user_code.py
from cachetools.ttl import TTLCache

With this:

python3 -Wall user_code.py
/Users/wim/git/cachetools/user_code.py:2: DeprecationWarning: cachetools.ttl is deprecated, please use cachetools.TTLCache
  from cachetools.ttl import TTLCache

Without this:

$ python3 -Wall user_code.py
/Users/wim/git/cachetools/src/cachetools/ttl.py:5: DeprecationWarning: cachetools.ttl is deprecated, please use cachetools.TTLCache
  warnings.warn(

[codecov-commenter]

Codecov Report

Merging #226 (d2297fe) into master (8b9bbc4) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #226   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          556       556           
=========================================
  Hits           556       556           

Impacted Files	Coverage Δ
src/cachetools/cache.py	100.00% <ø> (ø)
src/cachetools/fifo.py	100.00% <ø> (ø)
src/cachetools/lfu.py	100.00% <ø> (ø)
src/cachetools/lru.py	100.00% <ø> (ø)
src/cachetools/mru.py	100.00% <ø> (ø)
src/cachetools/rr.py	100.00% <ø> (ø)
src/cachetools/ttl.py	100.00% <ø> (ø)

---

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