Add OPTIONS-method as a shortcut

[theikkila]

Axios is missing OPTIONS-method as a shortcut. This PR will implement it

[coveralls]

Coverage remained the same at 93.979% when pulling 2e0adc1 on theikkila:master into d982cf9 on mzabriskie:master.

[nickuraltsev]

Thank you for the PR! What's the use case for this?

[theikkila]

This is for making the API consistent across all standardized HTTP-verbs. Options is sematically used ie. when fetching dynamic options for some endpoint.
Usually the response can tell the allowed or required fields.

[ianks]

I would like to use this to test that my API is returning the correct CORS headers.

[nickuraltsev]

I don't think we need to add a shortcut method for OPTIONS as preflight requests are normally sent by the browser. For test purposes, you can use the request method as follows:

axios.request({
  method: 'options',
 url: '/foo'
})

Thank you!

[theikkila]

OPTIONS are not just related to preflight requests but also for actually inspecting meta-data about some REST api endpoint. OPTIONS-shortcut is not for preflight requests but as I said ie. to gather some options about the validation. So closing this PR for that is just wrong.

According to RFC-2616 / 9.2 OPTIONS:
https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html

The OPTIONS method represents a request for information about the communication options available on the request/response chain identified by the Request-URI. This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.

Real world example is Django Rest Framework, it uses the OPTIONS-verb exacly for that purpose.

Another reason to merge this PR is to make the API of axios consistent. All other RFC-verbs are implemented as shortcuts except this.

Please reopen this PR @nickuraltsev

[coveralls]

Coverage decreased (-0.3%) to 93.687% when pulling 2e0adc1 on theikkila:master into d982cf9 on mzabriskie:master.

[nickuraltsev]

The options method does not accept data parameter. Could you please remove data and place options between head and post in README.md?

[theikkila]

Yeah, sure!

[coveralls]

Coverage decreased (-0.3%) to 93.687% when pulling 8cdfcd0 on theikkila:master into d982cf9 on mzabriskie:master.

[theikkila]

Fixed reviewed problems. Also updated the documentation from instance methods to contain the new added alias.