Backports for Julia 1.5

[maleadt]

Includes new CUDNN interface.

[codecov]

Codecov Report

Merging #705 (b52b41d) into compat (02ac36a) will increase coverage by 1.82%.
The diff coverage is 65.72%.

@@            Coverage Diff             @@
##           compat     #705      +/-   ##
==========================================
+ Coverage   77.27%   79.10%   +1.82%     
==========================================
  Files         116      123       +7     
  Lines        6438     6705     +267     
==========================================
+ Hits         4975     5304     +329     
+ Misses       1463     1401      -62     

Impacted Files	Coverage Δ
lib/cudnn/CUDNN.jl	44.18% <ø> (+1.32%)	⬆️
lib/cudnn/tensor.jl	31.03% <31.03%> (-19.99%)	⬇️
lib/cudnn/util.jl	40.74% <40.00%> (-6.32%)	⬇️
lib/cudnn/batchnorm.jl	33.33% <42.85%> (ø)
lib/cudnn/pooling.jl	53.33% <51.72%> (-24.93%)	⬇️
lib/cudnn/reduce.jl	51.85% <51.85%> (ø)
lib/cudnn/softmax.jl	61.53% <58.33%> (-5.13%)	⬇️
lib/cudnn/nnlib.jl	59.41% <59.87%> (-4.23%)	⬇️
lib/cudnn/activation.jl	64.28% <64.28%> (-16.97%)	⬇️
lib/cudnn/rnn.jl	69.29% <69.29%> (+69.29%)	⬆️
... and 52 more

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