Add support for custom_fields editor and required fields #21

Currently the python SDK does not support
'custom_fields': '[{"name":"newline", "value":"$20,000", "editor":"Client", "required":true}]',
the editor and required fields for custom_fields. Please add this support.

The python SDK will work for templates and custom fields, but not in the case where you want to assign an editor or make it required.

Workaround:

import requests

buildTheRequest = 'https://' + apikey + ':@api.hellosign.com/v3/signature_request/create_embedded_with_template'

data = {
'client_id': 'YOUR_CLIENT_ID',
'template_id': 'YOUR_TEMPLATE_ID',
'subject': 'ticket214090',
'message': 'ticket214090',
'signers[Client][name]': 'George',
'signers[Client][email_address]':'YOUR_EMAIL',
'custom_fields': '[{"name":"newline", "value":"$20,000", "editor":"Client", "required":true}]',
'test_mode': '1'
}

print(buildTheRequest)

r = requests.post(buildTheRequest, data)
print(r.text)