add BlobFromImages

[WendelHime]

Hi guys, I'm trying to implement the #395 , someone can please review and make suggestions?

[codecov-io]

Codecov Report

Merging #467 into dev will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #467      +/-   ##
==========================================
+ Coverage   97.96%   97.98%   +0.01%     
==========================================
  Files          17       17              
  Lines        1968     1984      +16     
==========================================
+ Hits         1928     1944      +16     
  Misses         33       33              
  Partials        7        7

Impacted Files	Coverage Δ
dnn.go	89.74% <100%> (+1.17%)	⬆️

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[WendelHime]

@deadprogram should I refactor blobFromImage to follow the opencv 4.1 specification?

[deadprogram]

There are 2 signatures as that function is overloaded and we already have implemented one of them. There is has been no change in that version, so the answer would be "no, that is not needed".

[deadprogram]

Also, thank you for the contribution! Now squashing/merging.

Thanks again!