config: add template support V2: - Limit escaping to plain formatting only - Use the formatter consistently (no more ui.debug) - Always include 'name' and 'value' V3: - Always convert 'value' to string (this also makes sure we handle functions) - Keep real debug message as ui.debug for now - Add additional tests. Note: I'm not quite sure about the best approach to handling the 'print the full config' case. For me, it printed the 'ui.promptecho' key at the end. I went with globs there as that at least tests the json display reliably. Example output: [ { "name": "ui.username", "source": "/home/mathias/.hgrc:2", "value": "Mathias De Maré <mathias.demare@gmail.com>" } ]