Add AutoScroller

[msaps]

Add PageboyAutoScroller class and autoScroller property to PageboyViewController, to allow for automatic time-based page scroll transitions. Resolved #3

[codecov]

Codecov Report

Merging #15 into develop will decrease coverage by -2.4%.
The diff coverage is 59.22%.

@@            Coverage Diff             @@
##           develop      #15     +/-   ##
==========================================
- Coverage    75.23%   72.83%   -2.4%     
==========================================
  Files           11       13      +2     
  Lines          630      729     +99     
==========================================
+ Hits           474      531     +57     
- Misses         156      198     +42

Impacted Files	Coverage Δ
Sources/PageboyTests/PageboyDataSourceTests.swift	85.5% <100%> (ø)	✅
Sources/Pageboy/PageboyScrollDetection.swift	56.97% <30%> (-1.67%)	❌
Sources/Pageboy/PageboyAutoScroller.swift	50% <50%> (ø)
Sources/Pageboy/PageboyViewController.swift	73.58% <69.23%> (-0.74%)	❌
Sources/PageboyTests/PageboyAutoScrollTests.swift	90% <90%> (ø)

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