Nth: addressing #136 - fixing -1 bug on slice of length 1.

[crunk1]

• Fixed incorrect Nth behavior for -1 index.
• More performant index checking (haven't tested, but removed Math.Abs call and casting to/from float64)

Used constraints.Integer for 'nth' parameter.
Panic instead of raising error on out of range.

[crunk1]

Addressing #136

[dolmen]

Too many changes which are not related to #136. For example you changed the Nth signature.

Please do separate PRs.

[crunk1]

@dolmen removed unrelated changes. Other changes are in PR #151

[codecov-commenter]

Codecov Report

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The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #137   +/-   ##
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  Coverage          ?   89.88%           
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  Files             ?       12           
  Lines             ?     1325           
  Branches          ?        0           
=========================================
  Hits              ?     1191           
  Misses            ?      132           
  Partials          ?        2           

Flag	Coverage Δ
unittests	89.88% <0.00%> (?)

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[samber]

Oops.

Thanks for the fix.