Save the trace of each parse while processing a duration.
Call for formatted dates the wrapper _set() instead of set()
in order to alter the modified counters.dateparse: when printing traces, print a trace for each object
returned.Add tests for the trace method and improve its documentation.
Document possible bugs and caveats.
Rename some variables with method name strings to be more
descriptive and also interpolate their strings initially.Substitute an expression for a block as used by 'map'.