Add Russian-Tatar United keyboard layout

This new layout made for those who use Russian layout all the time but sometimes need to write some Tatar text. It based on Russian layout and adds Tatar symbols to third layer. Also added symbols important for Russian typography as guillemets and emdash. Finally, symbols from Latin layout that important for code writing.

Typographic symbols added as separated layout (ru_typo) and Russian-Tatar United layout is based on it.

Unfortunately I had to invent typographic layout myself because existing ones (like Birman layout) are too complicated, they include specialized symbols for math, currencies and typographic symbols for non-cyrillic languages. Also they utilize letter keys that make the layout hard to override with national symbols. So I made my own layout with only cyrillic typographic symbols and symbols from English (US) layout.

English layout symbols are needed for coding and other stuff like writing emails or tags in messengers (no @ and # symbols in Russian layout).

Article about this layout: https://800147.github.io/rtu/en