[swift-evolution] [Draft]: Introducing a striding(by:) method on 3.0 ranges

[Ben Rimmington]

Re: "Completing the Swift 3 range operator suite"
<https://gist.github.com/erica/af92c541a0fb69fce1b7aaf8374a5aa9>

The proposed operators (<.. and <.<) are not allowed by Swift 2.2 lexer grammar:

<https://github.com/apple/swift/commit/0bfacde2420937bfb6e0e1be6567b0e90ee2fb67>
<https://github.com/apple/swift/commit/d0256a50d0346f7d4b4c0054dddd0734febc6bb1>

-- Ben