Review Limiter interface

[k1LoW]

• Rename LimitError to Context.
• Accept Context straight away.
• Fix Context to retain the value of limitHandler at the time of
• Export Context fields for implementing Limiter

[github-actions]

Code Metrics Report

	main (c10a935)	#35 (c19212d)	+/-
Coverage	80.8%	79.5%	-1.3%
Code to Test Ratio	1:0.9	1:0.9	-0.0
Test Execution Time	16s	18s	+2s

Details

  |                     | main (c10a935) | #35 (c19212d) |  +/-  |
  |---------------------|----------------|---------------|-------|
- | Coverage            |          80.8% |         79.5% | -1.3% |
  |   Files             |              2 |             2 |     0 |
  |   Lines             |             78 |            73 |    -5 |
- |   Covered           |             63 |            58 |    -5 |
- | Code to Test Ratio  |          1:0.9 |         1:0.9 |  -0.0 |
  |   Code              |            219 |           214 |    -5 |
- |   Test              |            204 |           196 |    -8 |
- | Test Execution Time |            16s |           18s |   +2s |

Code coverage of files in pull request scope (80.8% → 79.5%)

Files	Coverage	+/-
context.go	50.0%	+50.0%
error.go	0.0%	-85.7%
rl.go	80.3%	0.0%

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Reported by octocov

[github-actions]

BenchmarkRL-2

	main (-)	#35 (c19212d)	+/-
Number of iterations	10000	10000	0
Nanoseconds per iteration	194273 ns/op	192010 ns/op	-2263 ns/op
Bytes allocated per iteration	18374 B/op	18409 B/op	35 B/op
Allocs per iteration	156 allocs/op	155 allocs/op	-1 allocs/op

Metadata

	main (-)	#35 (c19212d)
goos	linux	linux
goarch	amd64	amd64
pkg	github.com/k1LoW/rl	github.com/k1LoW/rl
cpu	Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz	Intel(R) Xeon(R) Platinum 8272CL CPU @ 2.60GHz

Cachegrind (./testdata/testbin/testbin 10000)

	main (-)	#35 (c19212d)	+/-
Ir	1170284541	45287258307	44116973766
I1mr	8693100	8656605	-36495
ILmr	5957	5963	6
Dr	332457311	14293582451	13961125140
D1mr	763554	729998	-33556
DLmr	14407	14026	-381
Dw	145631293	5450814868	5305183575
D1mw	619797	628025	8228
DLmw	72378	72416	38

Metadata

	main (-)	#35 (c19212d)
I1 cache	32768 B, 64 B, 8-way associative	32768 B, 64 B, 8-way associative
D1 cache	32768 B, 64 B, 8-way associative	32768 B, 64 B, 8-way associative
LL cache	8388608 B, 64 B, 16-way associative	8388608 B, 64 B, 16-way associative
cmd	./testdata/testbin/testbin 10000	./testdata/testbin/testbin 10000

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Reported by octocov