MNT: Improve exception handling

[pllim]

See PyCon 2019, May 4 talk by Mario Corchero on exception handling (https://www.youtube.com/watch?v=V2fGAv2R5j8).

From @ejeschke, "Interesting bits for logging start at 6:00, formatting exceptions content starts at 9:32. TLDW summary: you want to pass the exception object itself to a %r formatting code."

xref feccdb0#r35961668