Add `Counter` functions with ranges and offsets.

[ta0kira]

Right now it's too error-prone to use Counter.zeroIndexed to do ranges and offsets.

[ta0kira]

Rather than adding a bunch of named functions for different combinations, maybe it could use a builder, e.g.,

traverse (Counter.build().start(0).count(5).by(2) -> Int i) {
  // 0 2 4 6 8
}

traverse (Counter.build().start(10).finish(15) -> Int i) {
  // 10 11 12 13 14 15
}

traverse (Counter.build().count(n) -> Int i) {
  // same as Counter.zeroIndexed(n)
}

traverse (Counter.build().count(n).reverse() -> Int i) {
  // same as Counter.revZeroIndexed(n)
}