Update year range in LICENSE

results: Fix Headers encoding (tsenart#507)

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

This reverts commit 3629602.

* results: Fix headers encoding

results: Faster JSON encoding and decoding (tsenart#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 tsenart#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)
```

fix: fix module import path for Go module (tsenart#501)

* fix: fix module import path for Go module

* fix: fix Go import paths in code

report: Round duration to the next most precise unit

So that the width of the text report doesn't get out of hand.

Fix .goreleaser to work with new unified versioning

We no longer split library and cli versions.

attack: Add -max-workers flag (tsenart#421)

* attack: Add -max-workers flag

This commit introduces the `-max-workers` flag and associated function
options. This allows controlling the concurrency level that vegeta uses,
but can sacrifice reaching the requested `-rate`, in case the specified
max number of workers is below the what is needed to sustain such rate.

* Updated README

* Update README.md

attack: Measure latency when requests timeout (tsenart#404)

Fixes tsenart#402

Introduce Pacer interface, ConstantPacer and SinePacer. (tsenart#400)

* Introduce Pacer interface and ConstantPacer.

The Pacer interface allows vegeta's attack rate to be customized.
Attack code keeps track of the elapsed attack duration and the number
of hits sent and provides these to Pace, which must return a Duration
for the attack code to sleep for before sending the next hit. Pace may
also return true for the second stop value to terminate the attack.

This interface allows vegeta to model a wider range of attack scenarios,
such as diurnal request patterns or load-test behaviour, where the
attack rate increases until the target begins to serve errors.

* Add SinePacer, for sinusoidal attack rates.

SinePacer is a Pacer that describes attack request rates with the
equation Rate = Mean * Amplitude * sin(Offset + t * (2𝛑 / Period)).

Both the Mean and Amplitude rates are expressed with ConstantPacer.

attack: Measure latency when requests timeout (tsenart#404)

Fixes tsenart#402