(refactor) throttle foldCheck instead of debounce

[potench]

(refactor) throttle foldCheck for viewability during scrolling instead of debounce

fixes #44

Goal:

1. Checks viewability immediately on scroll, throttles for 20 ms, checks viewability on scroll.
2. Reduces latency of checking viewability on scroll.

[codecov]

Codecov Report

Merging #45 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
+ Coverage   93.04%   93.05%   +0.01%     
==========================================
  Files           8        8              
  Lines         575      576       +1     
==========================================
+ Hits          535      536       +1     
  Misses         40       40

Impacted Files	Coverage Δ
src/createManager.js	92.3% <100%> (+0.03%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7481c4d...2e00c1c. Read the comment docs.

[codecov]

Codecov Report

Merging #45 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
+ Coverage   93.04%   93.07%   +0.03%     
==========================================
  Files           8        8              
  Lines         575      578       +3     
==========================================
+ Hits          535      538       +3     
  Misses         40       40

Impacted Files	Coverage Δ
src/createManager.js	92.37% <100%> (+0.1%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ee26b0e...597b697. Read the comment docs.

[potench]

Changes Planned:
According to https://bundlephobia.com/result?p=debounce@1.0.2 lodash.debounce and lodash.throttle add 4kb in dependencies while debounce is only 400b.

Going to replace both with smaller libraries