Add ITP to docs/api.md (#222)

Author: devgru

docs/api.md

@@ -77,6 +77,7 @@ codebase: 'https://github.com/evercoder/culori/blob/main'
 <li><a href='#interpolatorSplineMonotoneClosed'>interpolatorSplineMonotoneClosed</a></li>
 <li><a href='#interpolatorSplineNatural'>interpolatorSplineNatural</a></li>
 <li><a href='#interpolatorSplineNaturalClosed'>interpolatorSplineNaturalClosed</a></li>
+<li><a href='#color-spaces'>itp</a></li>
 <li><a href='#color-spaces'>jab</a></li>
 <li><a href='#color-spaces'>jch</a></li>
 <li><a href='#color-spaces'>lab65</a></li>
@@ -1905,4 +1906,4 @@ __convertYiqToRgb__(_color_) → _color_ | `yiq` → `rgb`
 [kotsarekno-ramos]: http://www.progmat.uaem.mx:8080/artVol2Num2/Articulo3Vol2Num2.pdf
 [din99ode]: https://de.wikipedia.org/wiki/DIN99-Farbraum#Farbabstandsformel
 [midpoint]: https://github.com/w3c/csswg-drafts/issues/3935
-[eitp-difference]: https://www.itu.int/rec/R-REC-BT.2124/en
+[eitp-difference]: https://www.itu.int/rec/R-REC-BT.2124/en