* Fix unicode.split with seperators examples
https://nim-lang.org/docs/unicode.html#split.i%2Cstring%2CRune%2Cint didn't work with the set constructor `{}` so replaced it with a string that's converted to an openArray compatible type containing `Rune`s.
* Add runnableExamples to unicode.split
* Add runnableExamples to split with single separator too
* Simplify runnableExamples unicode.split
* Improve the rest of the runnableExamples with the simplified code
* Simplify runnableExamples of unicode.split even more
* Formatted unicode.split example
* Update lib/pure/unicode.nim
Co-authored-by: zetashift <rishi2@laptop.localdomain>
Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>