Need fromBytesThrow

[ndmitchell]

I wrote fst3 . Fdn.fromBytes Fdn.UTF8 because I'm lazy. I imagine lots of other people will to - but what I really want is to just throw errors and return good stuff.

Related, a readFileUTF8 would also be handy, since then I wouldn't have to fromBytes and since it's in IO anyway the fact it throws is no great shock.

[NicolasDP]

this does relate a bit to #312

[vincenthz]

agreed on readFileUTF8

also as a note, probably can do Foundation fst which should work on 3-tuple too.