Serializer abstract method names mixup

[anderssonjohan]

@Lxstr I got totally confused by this change 😅 First after using the code I realized the abstractmethods are mixed up. def dumps should be def loads and vice versa. (they are correct in the implementation on lines 129 and 137)

Originally posted by @anderssonjohan in 0c22ec6

Note: this concerns code still in the development branch