[Help/Suggestion] Adding floating point margins for more control

Help, or Suggestion if not possible

# Problem description

I'm using a padded view to make my content easier to read. However, margins must be a `usize` and `1` is still a little too big for my application. Is there a way to add floating point margins?

# Environment

* Operating system: macOS
* Backend: ncurses
* Current locale: en_US.UTF-8
* Cursive version: 0.12.0