handler: fixes queryparams variables

[chris-ramon]

Overview

• handler: fixes to use pointer instead to unmarshal correctly.
• request_options_test: adds test for sending query params.
• based various previous PR's: variables in the URL query string are now correctly unmarshalled #10, fix json.Unmarshal in getFromForm to use a pointer #13, fix: parse variables #15, Fix “variables” unmarshalling in getFromForm #16, Fix unmarshalling variables from form data #18, Fixed bug with variables of graphql query #22 — thanks a lot for your contribution 👍

Test plan

• Unit test.

[coveralls]

Coverage remained the same at 87.261% when pulling f1c10e5 on fix/variables-bug into 707d93f on master.