`takeWhile` , `dropWhile`, and more!

Added

Many equivalents to Kotlin standard library were added 🎉

• Reducers
  • iter.average() (inspired by Kotlin's sequences.average)
• Transformers
  • iter.takeWhile() (inspired by Kotlin's sequences.takeWhile)
  • iter.drop() (inspired by Kotlin's sequences.drop)
  • iter.dropUntil() (like iter.until() but drops til given predicate is true)
  • iter.dropWhile() (inspired by Kotlin's sequences.takeWhile)

Changed

• added tests for NaN checks in iter.sum() and iter.product().
• Simplified deno.json again using the new [global-exclude][global-exclude]
  feature.