Add to twinpack-registry

[stefanbesler]

Hey! Thanks for this string builder library, it's great! Do you mind adding it to twinpack-registry so I could download and install it via Twinpack?
Looks that it is pretty finished, despite having "only" pre-releases?

[fisothemes]

I may not do that just yet since the development of this library is still very early. I'm also planning on making a polished version of this for the Fs libraries I'm working on.