[swift-evolution] Strings in Swift 4

[Ben Rimmington]

<https://github.com/apple/swift/blob/master/docs/StringManifesto.md#f1>

> In practice, these semantics will usually be tied to the version of the installed ICU library, which programmatically encodes the most complex rules of the Unicode Standard and its de-facto extension, CLDR.

Unicode is released in June.             <http://www.unicode.org/versions/#schedule>
CLDR is released in March and September. <http://cldr.unicode.org/#TOC-General-Schedule->
ICU is released in April and October.    <http://site.icu-project.org/download>

Therefore "libicucore" on Apple platforms will always use an older Unicode standard.
For example, iOS 10 and macOS Sierra are using ICU 57, which doesn't support Unicode 9.

Could you include the latest ICU alongside the Swift standard library?

-- Ben