feat: allow setting full width and height

[josa42]

Allow setting the size to the full editor:

require('neo-zoom').setup({
  winopts = {
    offset = { top = 0, left = 0, width = 1, height = 1 },
    border = 'none',
  },
})

Demo

https://user-images.githubusercontent.com/423234/218317701-622d5137-6e5a-4073-8063-0ebaee554077.mov

[nyngwang]

@josa42 Hi, thanks for your contributions! Indeed, I realized that there is a bug in my original implementation when specifying either width or height to 1. I will create a commit with you as the author since I have pushed another commit which causes some conflicts.