add Keltner channel (ta.kc)

[tsuz]

Also fixes true range which was broken

[codecov]

Codecov Report

Merging #54 (1c4bf80) into main (2200f88) will decrease coverage by 0.11%.
The diff coverage is 84.21%.

❗ Current head 1c4bf80 differs from pull request most recent head 9e743cb. Consider uploading reports for the commit 9e743cb to get more accurate results

@@            Coverage Diff             @@
##             main      #54      +/-   ##
==========================================
- Coverage   81.72%   81.61%   -0.11%     
==========================================
  Files          26       27       +1     
  Lines        1592     1632      +40     
==========================================
+ Hits         1301     1332      +31     
- Misses        214      219       +5     
- Partials       77       81       +4     

Impacted Files	Coverage Δ
pine/series_kc.go	75.00% <75.00%> (ø)
pine/ohlcv_series_base.go	79.83% <100.00%> (+0.67%)	⬆️
pine/series_dmi.go	66.12% <100.00%> (ø)

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