Refactor documentation and identifiers' names

[kolayne]

Reread the whole code and bring both identifiers' names and documentation to a single style. Also, fix typos, language mistakes. It would be perfect to create a Markdown document describing the rules of our documenting style

[kolayne]

We are not yet ready to start, but I guess, we are ready to when #2 is merged

[kolayne]

TODO: add <br>s in the documentation where line breaks are expected because Doxygen ignores usual line breaks