Specify and implement parser tracing for debugging support

This is a broad feature for discussing the type of trace information logged by the parser for debugging purposes as well as the log format. The trace information should support (at minimum) a range of to-be-specified debugging features. I'll work on opening a wiki article for planning this feature in further detail, and use this issue for tracking progress.

Start by reviewing the issue and the planned wiki discussion, focusing on the debugging features the parser trace must support and the proposed log format. The work is done when the trace requirements and format are specified and the parser implementation supports the agreed design.

Written by the indexing model from the issue text.