Make default field substitutions for "-" and "."

The defaults are 'skip' for dash and 'print empty' for period.  This is kind of
experiemental.  I'm trying to find convenient usage patterns.
Revamp -cC to allow configurations; remove -dD

Practical usage suggests that it's handy to put the entire definnition for a
timeseries into a particular file.  This enables that use case.  The -dD
options don't yet jive with that setup so they are removed until they can be
updated too.
Use 'format' variable name instead of 'line_format'

This is a fairly inconsequential nicety when using -c: the format variable is
more natural to write in a config file.