Generate62RandomString creates a random string with the given length consisting of characters in [A-Za-z0-9].

GenerateFriendlyRandomString creates a random string of characters with the given length consististing of characters in [a-z0-9].

GenerateRandomString creates a random string of characters of the given length from the given dictionary of possible characters.

SavePost writes the given bytes to a file with a randomly generated name in the given directory.

FriendlyIdLen is the length of any saved posts's filename.