Added AssertIncreasing and AssertDecreasing

[floaust]

Fixes #30
Fixes #29

[codecov]

Codecov Report

Merging #43 (751fab3) into main (90cbc5e) will increase coverage by 0.65%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
+ Coverage   86.31%   86.96%   +0.65%     
==========================================
  Files          10       10              
  Lines         621      652      +31     
==========================================
+ Hits          536      567      +31     
  Misses         49       49              
  Partials       36       36              

Impacted Files	Coverage Δ
assert.go	93.95% <100.00%> (+0.70%)	⬆️

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