Logging

Want to log user activity for university course sites. Record log ins, node views (including time spent on page, if possible), exercise submissions, viewing feedback, other things. Need ability to add code for custom events (with, e.g., plugins). Include custom data in logs, like responses to questions embedded in nodes. Different log records will store different kinds of data, depending on the event. Might be in serialized arrays, JSON strings, or something else.