The Subsetter class now uses a module-level 'log', and no longer uses
its own custom Logger. This has been removed, and its features replaced
by equivalents.
log.lapse() are replaced with Timer context manager/decorator (these should make clearer where the elapsed time starts/stops);
log.glyphs() is kept for convenience: it is bound dynamically to the logger instance instead of subclassing logging.Logger, as it's only
useful in here.
log.font() is replaced by `font.saveXML(sys.stdout)`.
A distinct sub-logger is configured for timing messages, to allow --timing option to be enabled independently from --verbose
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