Add orthogonal and isparallel function

[lijas]

I have wanted this a couple of times :)

[codecov-commenter]

Codecov Report

Patch coverage: 73.33% and project coverage change: -0.30 :warning:

Comparison is base (96f6bfa) 98.22% compared to head (c82f4dc) 97.92%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
- Coverage   98.22%   97.92%   -0.30%     
==========================================
  Files          17       17              
  Lines        1238     1253      +15     
==========================================
+ Hits         1216     1227      +11     
- Misses         22       26       +4     

Impacted Files	Coverage Δ
src/Tensors.jl	94.44% <ø> (ø)
src/math_ops.jl	96.80% <73.33%> (-3.21%)	:arrow_down:

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[KnutAM]

Cool! Perhaps also the orthogonal can be generalized to 2nd order tensors?