fixedstring: a @safe, @nogc string type

[Moth]

hi all.

i got fed up with the built-in string type having so many 
features unavailable in `@nogc` code, so i made my own.

introducing fixedstring: a templated fixed-length array of 
`char`s, compatible with `@safe`, `@nogc`, and `nothrow` code.

licenced under the AGPL-3.0 or later, but i'm open to relicensing 
if someone really really wants it.

have fun =]

https://github.com/Moth-Tolias/fixedstring

special thanks to snarwin on the d discord for convincing me to 
post here.