Consider making verbs in `HttpMethods` as `const string` rather than `static readonly string`

[kchanlee]

When I am trying to use AcceptVerbsAttribute, I don't want to write verbs literally (e.g. [AcceptVerbs("GET", "POST")]) so I try to reuse the verbs defined in HttpMethods (e.g. [AcceptVerbs(HttpMethods.Get, HttpMethods.Post)]). But this is not acceptable by compiler.

How about making verbs in HttpMethods as const string rather than static readonly string so that they can be more widely used?

[khellang]

This has been discussed before; #712 (comment), but I think @davidfowl felt strongly that they should be static readonly for some reason.

[kchanlee]

@khellang Thanks for pointing it out. Let me close this issue.