String diff support

Make output like this easier to parse for humans, by showing at what position the strings differ:

Should have both the fields as values, and the default value.. Actual value was "Processor.%\ Utilisation,unit=% Core\ 1=0.03,Core\ 2=0.06,Core\ 3=0.139,value=1i 1435362189575692182" but had expected it to be "Processor.%\ Utilisation,unit=% Core\ 1=0.03,Core\ 2=0.06,Core\ 3=0.139,value=1i 1435362189575692182".

[cloudRoutine]

I’ve always found FParsec’s error messages particularly satisfying

Error in Ln: 1 Col: 10
[1] [2] [c]
         ^
Expecting: integer number (32-bit, signed)

so maybe something like

[Expected value was]                              
"Processor.%\ Utilisation,unit=% Core\ 1=0.03,Core\ 2=0.06,Core\ 3=0.139,value=1i 1435362189575692182"
                                                          ↑                                                    
                                                Error in Col: 59
[Actual value was]                                        ↓
"Processor.%\ Utilisation,unit=% Core\ 1=0.03,Core\ 2=0.06;Core\ 3=0.139,value=1i 1435362189575692182"

[Krzysztof-Cieslak]

I wouldn’t use [ and ] since it’s not used anywhere else.

But otherwise, looks good to me.