models: `.to_json` returns now `$oid:ID`
models: `Trst::Person::Firm` add Class-method `auto_search`
models: `BSON::ObjectId` issue
models: `Document#freights_list` fix #40
update CHANGELOG
bump version v0.3.1.1
Merge branch 'feature/v0.3.1.1' into develop,fix #38, #40