Features/326 maximum

[ClaudiaComito]

Analogue implementation to ht.minimum(). Solves Issue #326.

[codecov-io]

Codecov Report

Merging #328 into master will increase coverage by 0.02%.
The diff coverage is 98.33%.

@@            Coverage Diff             @@
##           master     #328      +/-   ##
==========================================
+ Coverage   96.77%   96.79%   +0.02%     
==========================================
  Files          53       53              
  Lines        8216     8336     +120     
==========================================
+ Hits         7951     8069     +118     
- Misses        265      267       +2

Impacted Files	Coverage Δ
heat/core/tests/test_statistics.py	100% <100%> (ø)	⬆️
heat/core/statistics.py	96.53% <96.07%> (-0.08%)	⬇️

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[ClaudiaComito]

I'm going to go ahead and merge this as it's identical to ht.minimum()