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

    timew start|stop [<tagset>]
    timew track <interval> [<tagset>]
    timew clear <tagset>|<interval>
    timew continue
    timew

    timew [<filter>] report <report>

    timew define holidays <locale>|none
    timew define holidays [work] <date>
    timew define week <day>[- <day>] [, <day>] ...
    timew define day [<day>] start|end <time>

    timew define tag <tag>
    timew define tag <tag> description <string>
    timew define tag <tag> start|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 define tag <tag> color <color>

    timew undo

    timew tags [<filter>]
    timew gaps [<interval>]
    timew extensions

    timew export [<interval>] [<tagset>]
    timew import <file>|- ...

    timew help [<command>|<keyword>|examples]
    timew diagnostics
    timew log mark|<string>


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

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

  timestamp: <day> <time>

  tagset:    <tag>+

  tag:       string


Intervals
---------
An interval defines a block of time, either using precise values, or vague
values that are interpreted according to context, yielding precise values. The
general form is:

  Precise:
    YYYY-MM-DDTHH:MM:SS[Z|±HH:MM]
    now
    8:23:00
    9am

  Vague (and precise interpretation):
    today                   :backfill - now      :active
    this morning            :backfill - 12:00:00
    last tuesday            YYYY-MM-DD :fill
    yesterday               YYYY-MM-DD :fill

An interval may be open ended:

      - B
    A - B
    A -
    A

When resolving an interval, vague terms are influenced by configured exclusions
and rules.  Precise terms _always_ override rules.


Tagset
------
A tagset is a set of unique UTF-8 strings, each indentifying some trackable
entity, for example:

  $ timew start Home Garden "Sprint 2016"
                ---- ------ -------------
                tag  tag    tag

                -------------------------
                tagset

Tags must be quoted if they contains spaces.


Keywords
--------
There are built-in and custom keywords, that look like this:

  :fill
  :quiet

They begin with a colon, and are heuristics for Timewarrior. They can override
feedback (:quiet) or offer guidance on how to create an interval (:fill). The
supported keywords are:

  :fill       Fill in gap
  :backfill   Fill in gap, backwards only
  :interrupt  Identify the interval as a temporary interruption
  :noreport   Prevent the interval being reported
  :quiet      No feedback
  :x          User defined


--- Raw Notes ---

- 'timew merge <file>' for combining data.  Or is this the same as
  'timew import <file>'?  Probably is.