[swift-evolution] [Pitch] Improve String Literals

[Ben Rimmington]

Re: <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md>

### Support escaping newlines in multi-line strings with a trailing `\`

Markdown can already be "hard-wrapped" in a multi-line string:
<https://daringfireball.net/projects/markdown/syntax#p>
Are there any better examples, to show the need for this feature?

### Adopt the C/Objective-C syntax that concatenates single-line strings

Concatenation of adjacent string literals in Swift
(which I think is handled by the *preprocessor* in C)
has a potential hazard [H2] identified by Peter Dillinger:
<https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170403/034897.html>

-- Ben