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.