refactor logs / grading tools

[parmentelat]

the logs as stored in ~/.nbautoeval were fine as long as only one kind or exercises were present

it is time to move to a more easily parsable format, using JSON first short time goal being to provide a basic generic discovery/parsing utility

see first rush in grading/grade-quizzes.py

among other desired features in an ideal world

• produce grades, of course
• provide a deadline after which results are ignored
• reset counters does not look useful

[parmentelat]

release 1.1.0 stores traces of student attempts as json in ~/.nbautoeval.trace

• quiz : only there
• exercises : temporarily keeps old and new tracing policies for easier deployments

post-processing tools remain to be written

[parmentelat]

situation has much improved with nbae-quiz-scan

no need for a deadline until now, so let's close this one