custom formatting idea: -t,--title FIELDS for a list of fields to format into title line

[trentm]

If I have some log output where one or a few common (and short) fields are typically present and I want to approach one line per log record, then I could use:

... | ecslog -t reqId

to put the reqId field in the title line. If/when have config file support, this could be a thing to add to custom formats.

[trentm]

A related idea from #15 discussion is:

• add a oneline format (title line, then render the rest all on the same line after the message), perhaps with a -1 shortcut flag

Then one could use ecslog -1i reqId to get the above. This isn't quite the same use case, however.

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Perhaps -T for this. I suspect I'll want -t ... for time format options (#17).