Use ordered maps

[fenollp]

Fixes #645

[bitomaxsp]

What kind of help is needed here? We (@northvolt) are super eager to see that released :)

[fenollp]

Hey @bitomaxsp I'd love some help! Right now I'm stuck solving this:

FAIL | Issue301 (0.00s)
     | panic: runtime error: invalid memory address or nil pointer dereference [recovered]
     | 	panic: runtime error: invalid memory address or nil pointer dereference
     | [signal SIGSEGV: segmentation violation code=0x1 addr=0x58 pc=0x805850]
     | goroutine 19 [running]:
     | testing.tRunner.func1.2({0x888260, 0xc6abe0})
     | 	/snap/go/10008/src/testing/testing.go:1396 +0x24e
     | testing.tRunner.func1()
     | 	/snap/go/10008/src/testing/testing.go:1399 +0x39f
     | panic({0x888260, 0xc6abe0})
     | 	/snap/go/10008/src/runtime/panic.go:884 +0x212
     | github.com/getkin/kin-openapi/openapi3.TestIssue301(0x0?)
     | 	/home/pete/wefwefwef/kin-openapi.git/openapi3/issue301_test.go:32 +0x250
     | testing.tRunner(0xc0001ac820, 0x947b40)
     | 	/snap/go/10008/src/testing/testing.go:1446 +0x10b
     | created by testing.(*T).Run
     | 	/snap/go/10008/src/testing/testing.go:1493 +0x35f
FAIL | 	github.com/getkin/kin-openapi/openapi3	0.005s

From there I believe the design satisfies me. The rest of the work should be straightforward(TM)!

Could you describe your needs WRT this patch a bit?

[takanuva15]

Hi, did you have any luck fixing this issue? Looks like I encountered the same circular reference problem when trying to use this library with a large complex schema like in #814

[renom]

Is it going to be merged?

[jedevc]

Hey @fenollp 👋 (fun to see you somewhere else from buildkit 🎉)

Is there anything I can do to help move this along? Really interested in preserving the order with this, and there currently doesn't seem to be a way to do it without this.

[fenollp]

Hey @jedevc ! Cool to find you here as well :)

This whole PR is about switching all maps accesses to a method API (Set, Value, Iter, ...)
Also, to use the methods everywhere, drop the direct maps accesses, drop the usage of sort package. Split things in multiple PRs if possible...

This is just a bunch of work I haven't had the time to get around to. If you (or anyone) wants to go ahead, I'll review PRs!