Add method name as argument for validating required fields with callable

[puentesarrin]

Hey @bodbdigr,

This pull request will allow us to use the request method name to check whether a field is required.
Update 1: It fixes an error when calculating the original request object when wrapping resources.
Update 2: It provides backward compatibility for overwritten dispatch() method that returns a 3-element tuple as a result.

Thanks!

[puentesarrin]

Hey @bodbdigr, after merging these changes to the master branch, could you please also create a tag with the name "0.3.9"?

[bodbdigr]

@puentesarrin yes, sure

[puentesarrin]

Thank you so much, @bodbdigr!