Convert maximum/minimum kwargs to max/min and warn

[tlambert03]

One deprecation warning slipped through after #60 ... for those using maximum and minimum kwargs on their widgets, this will catch those kwargs and turn them to max/min and show a warning

[codecov]

Codecov Report

Merging #82 (2037500) into master (f119363) will decrease coverage by 0.45%.
The diff coverage is 30.76%.

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
- Coverage   87.77%   87.31%   -0.46%     
==========================================
  Files          15       15              
  Lines        1619     1632      +13     
==========================================
+ Hits         1421     1425       +4     
- Misses        198      207       +9     

Impacted Files	Coverage Δ
magicgui/widgets/_concrete.py	80.46% <28.57%> (-1.75%)	⬇️
magicgui/widgets/_bases.py	89.11% <33.33%> (-0.69%)	⬇️

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[sofroniewn]

LGTM! One could consider aliasing to allow both, but not that big a deal either way. Probably easier just to stick to one for now

[tlambert03]

I think in the medium term, what I might like to do is let backends take a crack at parsing kwargs and returning them into a standardized magicgui form. That might let us "seem to" support both ipywidgets and qt, provided someone has done use_app('qt'). but yeah, something for later