Gets one/all field in a pipeline
		Args:
			pipeline_key 		key for pipeline
			field_key 			key for field (default: None i.e. ALL)
			returns				status code, field dict or list thereof

def get_pipeline_field(self, pipeline_key, field_key = None):
		'''Gets one/all field in a pipeline
		Args:
			pipeline_key 		key for pipeline
			field_key 			key for field (default: None i.e. ALL)
			returns				status code, field dict or list thereof
		'''
		uri = '/'.join([
						self.api_uri, 
						self.pipelines_suffix, 
						pipeline_key, 
						self.fields_suffix
						])
		if field_key:
			uri = '/'.join([uri, field_key])

		return self._req('get', uri)