Add benchmarks for all implemented headers except set-cookie.

Output of `cargo bench header`:

```
test header::common::accept::bench::bench_format             ... bench:       381 ns/iter (+/- 79)
test header::common::accept::bench::bench_parse              ... bench:       490 ns/iter (+/- 122)
test header::common::authorization::basic::bench_format      ... bench:       483 ns/iter (+/- 134)
test header::common::authorization::basic::bench_parse       ... bench:       334 ns/iter (+/- 162)
test header::common::authorization::raw::bench_format        ... bench:        98 ns/iter (+/- 21)
test header::common::authorization::raw::bench_parse         ... bench:        35 ns/iter (+/- 17)
test header::common::connection::close::bench_format         ... bench:        87 ns/iter (+/- 20)
test header::common::connection::close::bench_parse          ... bench:        76 ns/iter (+/- 16)
test header::common::connection::header::bench_format        ... bench:       107 ns/iter (+/- 23)
test header::common::connection::header::bench_parse         ... bench:       208 ns/iter (+/- 54)
test header::common::connection::keep_alive::bench_format    ... bench:       101 ns/iter (+/- 20)
test header::common::connection::keep_alive::bench_parse     ... bench:        92 ns/iter (+/- 19)
test header::common::content_length::bench::bench_format     ... bench:       109 ns/iter (+/- 23)
test header::common::content_length::bench::bench_parse      ... bench:        44 ns/iter (+/- 22)
test header::common::content_type::bench::bench_format       ... bench:       251 ns/iter (+/- 75)
test header::common::content_type::bench::bench_parse        ... bench:       219 ns/iter (+/- 63)
test header::common::cookie::bench::bench_format             ... bench:       440 ns/iter (+/- 116)
test header::common::cookie::bench::bench_parse              ... bench:       796 ns/iter (+/- 249)
test header::common::date::asctime::bench_format             ... bench:       553 ns/iter (+/- 108)
test header::common::date::asctime::bench_parse              ... bench:       317 ns/iter (+/- 108)
test header::common::date::imf_fixdate::bench_format         ... bench:       559 ns/iter (+/- 121)
test header::common::date::imf_fixdate::bench_parse          ... bench:       336 ns/iter (+/- 169)
test header::common::date::rfc_850::bench_format             ... bench:       532 ns/iter (+/- 188)
test header::common::date::rfc_850::bench_parse              ... bench:       365 ns/iter (+/- 168)
test header::common::host::bench::bench_format               ... bench:       157 ns/iter (+/- 32)
test header::common::host::bench::bench_parse                ... bench:        63 ns/iter (+/- 4)
test header::common::location::bench::bench_format           ... bench:        96 ns/iter (+/- 25)
test header::common::location::bench::bench_parse            ... bench:        56 ns/iter (+/- 13)
test header::common::server::bench::bench_format             ... bench:        91 ns/iter (+/- 33)
test header::common::server::bench::bench_parse              ... bench:        33 ns/iter (+/- 7)
test header::common::transfer_encoding::ext::bench_format    ... bench:        82 ns/iter (+/- 31)
test header::common::transfer_encoding::ext::bench_parse     ... bench:       151 ns/iter (+/- 32)
test header::common::transfer_encoding::normal::bench_format ... bench:       152 ns/iter (+/- 35)
test header::common::transfer_encoding::normal::bench_parse  ... bench:       209 ns/iter (+/- 163)
test header::common::upgrade::bench::bench_format            ... bench:       223 ns/iter (+/- 57)
test header::common::upgrade::bench::bench_parse             ... bench:       743 ns/iter (+/- 298)
test header::common::user_agent::bench::bench_format         ... bench:        98 ns/iter (+/- 31)
test header::common::user_agent::bench::bench_parse          ... bench:        37 ns/iter (+/- 14)
```