Specific configuration for methods invocations

[javierbrea]

In some scenarios could be desirable to modify configuration only for certain invocations to the provider methods. (For example, when passing an "idempotency-key" as an http header using "mercury-api" read method)

This options could be passed as a parameter to the "read" method, and should overwrite instance options only for that execution. For other methods, such as "create" or "update", options could be passed as second argument.

[javierbrea]

This issue was originally created at XbyOrange/mercury#33. That project seems to be no longer maintained, so it should be fixed in this one.

[javierbrea]

Parameters in read method are allowed from the v2.0.0 version, released in #37