refactored Unmarshal to use unmarshalValue which returns reflect.Value

needed for unmarshaling into reflect-created slices
initial implementation of REST's index route
implemented REST GET method
REST api now is a class, uses interface DataSource instead of lambdas
log errors in REST
initial implementation of POST route
add OPTIONS endpoint
respond with created object when POSTing
AddResource now takes an empty struct as first parameter
implemented DELETE
OPTION all the things!
200 -> 204 for OPTIONS
more refactoring of Unmarshal
wip