teken, vt(4): Parse the "Cursor style" escape sequence

teken, vt(4): Parse the "Cursor style" escape sequence

The escape sequence (e.g. `^[[2 q`) was unsupported before and the
letter `q` was displayed as a typed character. The sequence is used by
Neovim for instance.

Now, it is properly parsed. However, it is ignored, so it won't change
the cursor style.

Because the escape sequence contains a space character, the
`gensequences` script had to be modified to support that. In the
`sequences` file, a space is represented as the string `SP`.