Support more character formatting

[ghost]

Currently the editor supports bold, italic and underline. But the following are also useful for writing, including literature:

• Superscript. Useful in math (1 googol = 10¹⁰⁰) but also in some languages: in French, honorifics use superscript, e.g M^elle Juliette.

• Subscript. For example in chemistry (H₂O).

• Strikethrough for annotations, e.g: The dog and the cat ~was~were fighting.

• Small caps. Good for long acronyms, PA announcements and "writing on the wall". Example from James S.A Corey's Tiamat's Wrath: