PEP8+Better JSON-LD support

* The API has also changed, there are new parameters to send the
context as part of the headers.
* Improved tests
* PEP8 compliance (despite the line about gevent)

tests/sleep_plugin/sleep.py

@@ -2,7 +2,9 @@ from senpy.plugins import SenpyPlugin
 from senpy.models import Response
 from time import sleep
 
+
 class SleepPlugin(SenpyPlugin):
+
     def __init__(self, info, *args, **kwargs):
         super(SleepPlugin, self).__init__(info, *args, **kwargs)
         self.timeout = int(info["timeout"])