Added FlatBuffers#7

*This PR is based on the PR #6.* ``` running 19 tests test capnp_deserialize ... bench: 153 ns/iter (+/- 9) = 2928 MB/s test capnp_deserialize_packed ... bench: 456 ns/iter (+/- 21) = 739 MB/s test capnp_populate ... bench: 473 ns/iter (+/- 56) test capnp_serialize ... bench: 26 ns/iter (+/- 1) = 17230 MB/s test capnp_serialize_packed ... bench: 392 ns/iter (+/- 67) = 859 MB/s test clone ... bench: 194 ns/iter (+/- 22) = 2701 MB/s test flatbuffers_deserialize ... bench: 0 ns/iter (+/- 0) = 472000 MB/s test flatbuffers_populate_with_args ... bench: 599 ns/iter (+/- 35) test flatbuffers_populate_with_builder ... bench: 576 ns/iter (+/- 84) test flatbuffers_serialize ... bench: 0 ns/iter (+/- 0) = 472000 MB/s test rmp_serde_deserialize ... bench: 869 ns/iter (+/- 52) = 330 MB/s test rmp_serde_serialize ... bench: 273 ns/iter (+/- 6) = 1051 MB/s test rust_bincode_deserialize ... bench: 730 ns/iter (+/- 40) = 547 MB/s test rust_bincode_serialize ... bench: 179 ns/iter (+/- 15) = 2234 MB/s test rust_protobuf_deserialize ... bench: 566 ns/iter (+/- 61) = 505 MB/s test rust_protobuf_populate ... bench: 350 ns/iter (+/- 54) test rust_protobuf_serialize ... bench: 508 ns/iter (+/- 24) = 562 MB/s test serde_json_deserialize ... bench: 1,402 ns/iter (+/- 942) = 431 MB/s test serde_json_serialize ... bench: 1,289 ns/iter (+/- 49) = 469 MB/s test result: ok. 0 passed; 0 failed; 0 ignored; 19 measured; 0 filtered out ```