utf8-text: Mutable & Immutable utf8-text

WIP.

Turn back while you still can, here be segfaults.

1. I have not tested this.
2. You are afraid of this code.
3. Every line is unsafe.
4. Do not read the code here.
5. Code here WILL make your computer VERY UPSET.
6. You don't want this code.
7. This code is haunted.