Add comment to Ini structure

[FreeCX]

This code (example syntax)

let ini = Ini::new()
  .add_comment("This is comment before section")
  .section("params")
  .add_comment("This is comment before item")
  .item("foo", 3.14)
  .item_with_comment("bar", 2.71, "inline comment");

generate (after serialization)

; This is comment before section
[params]
; This is comment before item
foo = 3.14
bar = 2.71 ; inline comment