v4 major release

A major version v4 release of circuit library. See the changes in this PR: #121

For an up to date guide on upgrading v3 -> v4, see https://github.com/cep21/circuit/blob/master/UPGRADE_GUIDE.md.

A short list of changes are:

• Drop support for Gopkg.toml
• Remove the "/v3" root directory
• Move statsd implementation to another library
• Add ctx to the stats interfaces
• Move benchmarks to their own repo
• Use Go's built in atomic package
• Add upgrade guide

Add AfterFunc configuration for testing

Add AfterFunc configuration option to hystrix.ConfigureCloser (#111)

* Add AfterFunc configuration option to hystrix.ConfigureCloser

* Add AfterFunc field to ConfigureCloser Merge function

* Add json tag to omit AfterFunc from json encoding

Signed-off-by: Chris Guiney <chrisg@tune.com>

Co-authored-by: Chris Guiney <chrisg@tune.com>

Reduced imports

Reduce number of imports by giving benchmarking exclusive go.mod.

Support changing IsInterrupt behavior

Zuzmic treat deadline expired as failure (#95)

* treat DeadlineExceeded as failure

* remove comment: typo alrady fixed

* add IsErrInterrupt config option

* remove mutex

* fix ordering

* circle/circuit

Co-authored-by: Kolokhanin Roman <rkolokhanin@ozon.ru>

Copy license file

I copy the license file to v3 directory so pkg.go.dev can see it correctly.

Add Error interface for type casting

Merge pull request #78 from cep21/pr

Error: add Error type.

Modules should work better

Slowly figuring out all the go module corner cases for the right way to do this.

Support golang mod file

Supports a golang module file

Bug fix config setting while live

Pr53 with unit tests (#54)

* SetConfigThreadSafe should set notThreadSafeConfig to new config first

Change-Id: Ib8cde17faa1054e511d64ad23199ef519dc7e307

* Add unit test for setting circuit config

* Expand config unit test

Check the before and after state to make sure it changed

Allow setting statsd metric sanitizer

Allow people to sanitize their own statsd names. (#37)

People can pick how they want to sanitize statsd metric names