CLI Syntax
----------
The CLI shall have a well-defined and unambiguous grammar.

    timew start [<tagset>]
    timew stop [<tagset>]
    timew track [<interval>] [<tagset>]
    timew [<filter>] report <report>
    timew <filter> clear
    timew

    timew define holidays <locale>
    timew define holidays work <date>
    timew define week <day>[- <day>] [, <day>] ...
    timew define day start <time>
    timew define day end <time>
    timew define day <day> start <time>
    timew define day <day> end <time>

    timew define tag <tag>
    timew define tag <tag> description <string>
    timew define tag <tag> start <date>
    timew define tag <tag> end <date>
    timew define tag <tag> budget <number> <units> per <unit>
    timew define tag <tag> budget <number> <units> total
    timew define tag <tag> overlap

    timew export ...
    timew import ...

    timew help ...


CLI Grammar
-----------
Assumed built-in types:
  <datetime>
  <time>
  <duration>
  <string>

  interval:  <timestamp> "-" <timestamp>
             <timestamp> "to" <timestamp>
             "from" <timestamp> "to" <timestamp>
             "until" <timestamp>
             "from" <timestamp>

  timestamp: <day> <time>

  tagset:    <tag>+

  tag:       string


Rules Grammar
-------------
TBD.

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