[error] Allow find cause and inspect error without checking key words in error message

[at15]

Currently, error handling is still not very handy, still need to

• get root cause/cause of certain error, we already has wrap (but we have multi error)
• allow library user to inspect the error without calling strings.Contains(err.Error(), "not exists")
• categorize error so they can be reported to a central service (like sentry)
• convert error from standard library and pkg/errors
• document and example
  • auto update godoc.org after commit (it needs manual refresh ...)

Ref

Go

• Gopher China 2017 参会小结 sivagao/blog#47 mentioned methods like Timeout() in net package
  • https://blog.golang.org/errors-are-values
• https://github.com/moby/moby/tree/master/errdefs use interface like NotImplemented as causer
• • https://github.com/pingcap/tidb/tree/master/terror have class of error
• hashicorp's error package has some util function for traversing wrapped error Contains etc.
• https://github.com/getsentry/raven-go
• https://github.com/aws/aws-sdk-go/tree/master/aws/awserr

Rust

• https://github.com/rust-lang-nursery/failure
• https://doc.rust-lang.org/book/second-edition/ch09-00-error-handling.html

[at15]

@gaocegege @codeworm96 any recommendation for error handling in go/rust or any other languages ... @xplorld

[codeworm96]

I think errors should be type rich.

[at15]

@codeworm96 you mean have an interface and inspect based on type?

[codeworm96]

Different errors should be different types/variants of enum (at best effort, though)

[at15]

Fixed in #96