Update README with several features
Update README with several features

Added xflatten, get_names, get_types functions for compiled schema.
Added service_fields for compile options and as optional get_names,
get_types parameter.

tarantool/tarantool-avro,tarantool/tarantool-avro,tarantool/tarantool-avro,tarantool/tarantool-avro,tarantool/tarantool-avro,tarantool/tarantool-avro,tarantool/tarantool-avro