Update item struct to match paypal model (plutov#129)

* Update item struct to match paypal model

* test

Update payment capture response type to include links (plutov#128)

Add partner overrides to referral request (plutov#124)

* Add partner overrides to referral request

Add this object:
https://developer.paypal.com/docs/api/partner-referrals/v2/#definition-partner_configuration_override

* Update types.go

Add types to support Partner Referral API (plutov#123)

* Add types to support Partner Referral API

Add in the type structs to allow a POST call to v2/customer/partner-referrals
It sends a ReferralRequest, and returns a response of type Resource with only Links populated
https://developer.paypal.com/docs/api/partner-referrals/v2/

* Pointer for optional field

* Update types.go

Co-Authored-By: Roopak Venkatakrishnan <roopak.v@gmail.com>

Add Webhook data types (plutov#120)

* Add Webhook data types

Add the Event data types for payment capture and merchant onboarding events, which are sent for PayPal Commerce Platform integrations.

* remove unnecessary empty line

* name change and points for omitempty objects

* Update types.go

Co-Authored-By: Roopak Venkatakrishnan <roopak.v@gmail.com>

Fix authorizations (plutov#119)

Fix authorizations

Reset after reading (plutov#118)

Add verify webhook signature response (plutov#117)

Merge pull request plutov#115 from plutov/roopakv/fix_auth_capture

Fix payment capture API

Example for go modules in Readme (plutov#111)