Don't coerce json to a binary string on Py3
Fix failing test
Add "many" parameter to `dump` and `load`
dict_class is a property
Simplify implementation of Nested#_serialize
Only update fields once when serializing nested objects
set_class is also a property
Merge branch 'feat/dump-many' into dev
Document update_fields parameter
Add more test cases for loading nested data
No need to pass in `obj` argument to nested Schema constructor

That parameter will soon be removed
Update docs

A more illustrative intro example; fix typos and errors, simplify
Flask example