MD5: add structured answer
Sort: add structured answer.
DaysBetween: add structured answer
FlipText: use structured answer.
Chars: use structured answer.
Password: add structured answer.

Also, a nearly-complete rewrite to make it works as intended, while
still being easy to follow.
MakeMeASandwich: sudo use structured answer.
Atbash: update with structured answer
HexToDec: add structured answer.
Reverse: add structured answer.
EmToPx: use structured answer.
TwelveOclock: add structured_answer.
URLDecode: add structured_answer.
URLEncode: add structured answer
Fibonacci: use structured answer.
EmailValidator: use structured answer.
PigLatin: add structured answer.
GreatestCommonFactor: use structured answer.
CallingCodes: use structured answer.
Paper: use structured answer