Update the grader protocol documentation GRADERS.md

[markkuriekkinen]

GRADERS.md is a bit outdated.

• Not all HTTP GET query parameters are listed there
  • Relevant code that sets parameters:
    

    a-plus/exercise/exercise_models.py

    Lines 1019 to 1035 in a932c51

    	def _build_service_url(self, language, students, ordinal_number, url_name, submission_url, lti_launch_id=None):
    	"""
    	Generates complete URL with added parameters to the exercise service.
    	"""
    	uid_str = '-'.join(sorted(str(profile.user.id) for profile in students)) if students else ''
    	params = {
    	"max_points": self.max_points,
    	"max_submissions": self.max_submissions,
    	"submission_url": build_aplus_url(submission_url),
    	"post_url": build_aplus_url(str(self.get_url(url_name)), user_url=True),
    	"uid": uid_str,
    	"ordinal_number": ordinal_number,
    	"lang": language,
    	}
    	if lti_launch_id:
    	params["lti_launch_id"] = lti_launch_id
    	return update_url_params(self.get_service_url(language), params)

• ExerciseWithAttachment is deprecated and nobody is supposed to use it.

In addition, there are these documents:

• https://apluslms.github.io/protocols/aplus-assess-v1/
• https://apluslms.github.io/protocols/

They include some details that have never been implemented so that can lead to confusion. At any rate, take a look and compare if there are significant differences and something clearly outdated.