default instance for IsString

[Evan Laforge]

> The only reason I don't like using OverloadedStrings
> for typing string literals as Text and ByteString
> is that when you turn on OverloadedStrings, you turn
> it on for all types, not just Text and ByteString.
> I don't want to be forced to do that. Because
> all other uses of OverloadedStrings that I have
> seen, and there are many, are ill-advised in my
> opinion. They all should have been quasiquoters.

Could you name some names here?  Regardless of how this whole thread
goes, maybe people will agree that those uses were indeed ill-advised,
and we can get them fixed up.

Perhaps the problem is that fromString is very easy to understand and
write, but quasi-quoters sound like a whole new complicated thing to
learn about.  If we could either demonstrate that they're not so bad
to write, or have a little library that makes them easier for
"stringlike" things, then maybe we could move the first instinct away
from "hack a quick fromString" to "hack a quick QQ".