Resolves #37 - Unit test to validate resource docs links

[jccl]

No description provided.

[jccl]

The new test case will fail with following:

$ go test -timeout 30s -run ^TestResourceDocsExist$ github.com/elasticpath/epcc-cli/external/resources
--- FAIL: TestResourceDocsExist (3.48s)
    resources_yaml_test.go:35: Error Retrieving Link
        Link: ????/https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/create-an-event.html
        Error Message: Head "????/https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/create-an-event.html": unsupported protocol scheme ""
        Reference Count: 5
    resources_yaml_test.go:35: Error Retrieving Link
        Link: ????/https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/get-event-logs.html
        Error Message: Head "????/https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/get-event-logs.html": unsupported protocol scheme ""
        Reference Count: 3
    resources_yaml_test.go:35: Error Retrieving Link
        Link: ????/https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/get-event-logs.html#get-get-jobs-for-an-event
        Error Message: Head "????/https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/get-event-logs.html#get-get-jobs-for-an-event": unsupported protocol scheme ""
        Reference Count: 3
    resources_yaml_test.go:38: Unexpected Response
        Link: https://documentation.elasticpath.com/commerce-cloud/docs/api/advanced/events/create-an-event.html
        Expected Status Code: 200
        Actual Status Code: 404
        Reference Count: 1
    resources_yaml_test.go:38: Unexpected Response
        Link: https://documentation.elasticpath.com/commerce-cloud/docs/api/customers-and-accounts/account-management/accounts/get-an-account.html
        Expected Status Code: 200
        Actual Status Code: 404
        Reference Count: 1
FAIL
FAIL    github.com/elasticpath/epcc-cli/external/resources      3.484s
FAIL