Initial support for serde

[erickt]

Hello!

This PR adds initial support for serde. One of the cool things about it is that it can directly deserialize into a structure instead of having to go through cbor::Decoder to parse out a Cbor type and then deserialize from that into a cbor::RustcDecoder. It currently passes the tests and benchmarks pretty well (although it's still slower than serde_json for some unknown reason):

     Running target/release/bench-d76ac9f7d864696a

running 16 tests
test decode_medium_cbor        ... bench:  15,151,437 ns/iter (+/- 1,104,258) = 26 MB/s
test decode_medium_direct_cbor ... bench:   4,477,213 ns/iter (+/- 511,434) = 89 MB/s
test decode_medium_json        ... bench:  20,373,353 ns/iter (+/- 2,205,575) = 27 MB/s
test decode_small_cbor         ... bench:       1,315 ns/iter (+/- 37) = 30 MB/s
test decode_small_direct_cbor  ... bench:       2,558 ns/iter (+/- 345) = 15 MB/s
test decode_small_json         ... bench:       1,880 ns/iter (+/- 367) = 29 MB/s
test encode_medium_cbor        ... bench:     945,316 ns/iter (+/- 16,675) = 422 MB/s
test encode_medium_json        ... bench:   7,628,975 ns/iter (+/- 339,718) = 74 MB/s
test encode_medium_tojson      ... bench:  14,429,221 ns/iter (+/- 1,244,292) = 39 MB/s
test encode_small_cbor         ... bench:       3,460 ns/iter (+/- 359) = 11 MB/s
test encode_small_json         ... bench:         841 ns/iter (+/- 318) = 66 MB/s
test encode_small_tojson       ... bench:       1,213 ns/iter (+/- 202) = 46 MB/s
test read_medium_cbor          ... bench:   9,462,908 ns/iter (+/- 1,028,207) = 42 MB/s
test read_medium_json          ... bench:  14,876,985 ns/iter (+/- 2,433,638) = 38 MB/s
test read_small_cbor           ... bench:         785 ns/iter (+/- 193) = 50 MB/s
test read_small_json           ... bench:       1,226 ns/iter (+/- 26) = 45 MB/s

test result: ok. 0 passed; 0 failed; 0 ignored; 16 measured

     Running target/release/bench_serde-7de34a6bd2bc4f3a

running 8 tests
test deserialize_medium_cbor ... bench:   6,434,673 ns/iter (+/- 412,666) = 62 MB/s
test deserialize_medium_json ... bench:   4,808,781 ns/iter (+/- 1,297,244) = 117 MB/s
test deserialize_small_cbor  ... bench:       2,666 ns/iter (+/- 891) = 15 MB/s
test deserialize_small_json  ... bench:         439 ns/iter (+/- 16) = 127 MB/s
test serialize_medium_cbor   ... bench:   1,421,697 ns/iter (+/- 475,204) = 281 MB/s
test serialize_medium_json   ... bench:   4,730,402 ns/iter (+/- 1,666,983) = 120 MB/s
test serialize_small_cbor    ... bench:       3,479 ns/iter (+/- 491) = 11 MB/s
test serialize_small_json    ... bench:         441 ns/iter (+/- 122) = 126 MB/s

test result: ok. 0 passed; 0 failed; 0 ignored; 8 measured

     Running target/release/cbor-8d79df739e5d6e87

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured

Along the way I also changed how variants are serialized. Instead of {"variant": "Name", "fields": [...]}, it's now {"Name": [...]}. This is much more efficient for serde to parse because it doesn't require potentially buffering the field argument.

Be aware though that this does add a testing dependency to serde_macros, which is currently nightly-only. Check out how serde_tests in https://githb.com/serde-rs/serde if you're interested in a method that's compatible with stable rust.

[BurntSushi]

Sorry for dropping the ball on this one. I'm definitely not keen on requiring nightly to compile cbor. I'll have to find time to look into supporting this optionally and/or pick a stable approach.

[erickt]

Oh I thought I wrote this patch to only require the tests to be on nightly. Silly me! I'll fix it

[DeflateAwning]

Hmm what's the state of this? Would be awesome to be able to use this!

[BurntSushi]

@DeflateAwning Please read the README.