lib,cmd: add Dan as contributor for -connect-to

Previous commit didn't use Co-authored-by properly.

Co-authored-by: Dan Kegel <dank@kegel.com>

lib: use fixed IP selection function

Last release introduced a fixed firstOfEachIPFamily function, but didn't
integrate it.

lib: fix IP selection in DNS caching

Fixes #677

attack: support IPv6 only in DNSCaching

The previous code had a bug that assumed we could always find an IPv4
first.

Fixes #649

Signed-off-by: Tomás Senart <tsenart@gmail.com>

Signed-off-by: Tomás Senart <tsenart@gmail.com>

Signed-off-by: Tomás Senart <tsenart@gmail.com>

Update year range in LICENSE

results: Fix Headers encoding (#507)

* Revert "results: Faster JSON encoding and decoding (#506)"

This reverts commit 3629602.

* results: Fix headers encoding

results: Faster JSON encoding and decoding (#506)

* Add .idea to .gitignore

* results: Faster JSON encoding and decoding

This commit improves the performance of JSON encoding and decoding of
`Results`. Additionally, it fixes a regression introduced in #474 that
didn't produce valid JSON for HTTP headers. A test is added that
validates the JSON encoding matches the one produced by the
`encoding/json`.

```
name                            old time/op    new time/op    delta
ResultEncodings/json-encode-16     690ns ±12%     297ns ± 0%   -56.94%
(p=0.000 n=9+9)
ResultEncodings/json-decode-16    1.05µs ± 1%    0.03µs ± 1%   -97.47%
(p=0.000 n=10+8)

name                            old alloc/op   new alloc/op   delta
ResultEncodings/json-encode-16      804B ±87%        0B       -100.00%
(p=0.000 n=9+10)
ResultEncodings/json-decode-16      310B ± 0%        0B       -100.00%
(p=0.000 n=10+10)

name                            old allocs/op  new allocs/op  delta
ResultEncodings/json-encode-16      4.00 ± 0%      0.00       -100.00%
(p=0.000 n=10+10)
ResultEncodings/json-decode-16      4.00 ± 0%      0.00       -100.00%
(p=0.000 n=10+10)
```