Add the option to display a diff when comparing strings

[SuperFola]

Expected Behavior

ut::diff_onerror(that % mystring == otherstring) could display a diff of mystring vs otherstring

Actual Behavior

that % mystring == otherstring will print some hard to read text when dealing with multiline strings:

Running test "output a correctly formatted code for calls"... FAILED
in: /Users/fola/Documents/ArkScript/Ark/lib/ut/include/boost/ut.hpp:2961 - test condition:  [(let newlist (list:filter _listeners (fun (element) (!= typ (@ element 0)))))

# a badly aligned method below
# this comment bloc is also a test
(list:forEach
  _listeners
  (fun (element)
    (if (= typ (@ element 0)) {
      ((@ element 1) val)
      (set found true) })))
 == (let newlist (list:filter _listeners (fun (element) (!= typ (@ element 0)))))


# a badly aligned method below
# this comment bloc is also a test
(list:forEach
  _listeners
  (fun (element)
    (if (= typ (@ element 0)) {
      ((@ element 1) val)
      (set found true) })))
]

Here there is a new line that shouldn't be there in the second sample, which is quite hard to spot

Steps to Reproduce the Problem

1. create a test with boost::ut
2. compare two (different) strings

Specifications

• Version: 2.0.1
• Platform: macos
• Subsystem: