feat: Proper floating window for keymap help and OutlineStatus

No more obnoxious '}' on the cmdline when pressing `?`!

scope:
- More type hints
- Added class Float for creating floating windows with size that fit the
  content and position centered on the screen
- show_help action for outline window (key `?`) now uses a floating
  window
- :OutlineStatus now provides better information, and shows content in a
  floating window.

future:
- Floating window option configuration

lua/outline/config.lua

@@ -261,11 +261,6 @@ function M.get_providers()
   return M.providers
 end
 
-function M.show_help()
-  print('Current keymaps:')
-  print(vim.inspect(M.o.keymaps))
-end
-
 ---Check for inconsistent or mutually exclusive opts.
 -- Does not alter the opts. Might show messages.
 function M.check_config()