List of changes:
* Use thrift plugin compiler 0.3.0
* Update build_tools to latest
* Update build image to Erlang 21
* Added execution_start_time, execution_end_time, execution_duration_ms to woody state
* start using build_utils
* simplify woody_client:result_ok() type (issue 10)
* use integer snowflake id
* rename woody_client_thrift:format_return/3 (issue 11)
* provide details to event_handler for http errors (issue 15)
* clarify net_opts() for woody_server_thrift_http_handler:options() type
* switch snoflake to rbkmoney fork
* update readme
* introduce lint and fix lint warnings
* add woody_client:make_id_int/0 API function