String literals should be constant

[brson]

Currently string literals are allocated and copied from constant C strings on instantiation, which is quite wasteful.

[marijnh]

I agree that it's unfortunate for string literals to be non-constant. Unless we give them type @str, there doesn't seem to be a way around this though. Raw new-style strings own their memory. Whether that's a good idea is another discussion, but in this system you can't reuse string values.

[graydon]

Subsumed into #2112, closing.