Feature request: concatenate adjacent strings

[yawaramin]

E.g. like in C or Python:

let hello = "Hello, " "World!"; // = "Hello, " ++ "World!"

This would make it convenient to break up a long string into multiple lines in the source code, without introducing line breaks in the resulting string. E.g.:

let doc =
  "This command lets you "
  "do XYZ.";