Adjust some exercise numbers
Refactor slices exercise
Maps exercise number is now 43, also cleaned it up a bit
Fibonacci exercise is now 46
Complex cube roots exercise is now number 50
Errors exercise is now number 58
Http handler exercise is now number 60, also make it work from within VMs / containers
Images exercise is now number 62
ROT13 exercise is now number 63
Equiv binary tree is now number 72
Web crawler exercise is now number 73
I really tried to get the web crawler to work in parallel but I cant with my current knowledge... I'll just add the reference solution so I can find it easier in the future