Add option to truncate spec to window

[AntoinePrv]

Thank you for this great project!

When the cursor is close to a window border and the width is large enough, the specs / floating windows will be displayed above the sign column, or even another window.
Woud it be feasible to add an option to truncate the specs to the current window ? It would check the dimensions from the resizer and crop it.

I'm happy to send a PR, but I'm a bit short on time right now.