Trylle

#605 jsonpb.Unmarshal correctly handles escaped strings for some of the well-known types

#627 jsonpb.Unmarshal correctly returns an error when trying to marshal a scalar enum into repeated enums.

#630 jsonpb.Unmarshal correctly handles string versions of numeric primitives

#644 jsonpb.Unmarshal correctly handles enum values in maps

#624 fixes a performance regression where nested maps led to quadratic behavior

#628 reverts strict UTF-8 validation for proto2 string fields

#660 makes UTF-8 validation errors for proto3 string fields non-fatal