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

    timew
    timew start [<date>] [<tagset>]
    timew stop [<date>] [<tagset>]
    timew track <filter>
    timew clear <filter>
    timew continue

    timew [report] <report> [<filter>]
    timew day [<filter>]
    timew week [<filter>]
    timew month [<filter>]

    timew config [<name> [<value>]]
    timew undo

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

    timew export [<filter>]
    timew import <file>|- ...

    timew help [<command>|<keyword>|hints|examples]
    timew diagnostics


Filter
------
A filter is a combination of an <interval> and <tagset>, both being optional.

An interval is a representation of a time range with tags.

  <interval>:
    ["from"] <date> ["to"|"-" <date>]
    ["from"] <date> "for" <duration>
    <duration> ["before"|"after" <date>]

Examples of an interval:

    2016-04-15
    29th
    since socm
    yesterday
    from yesterday to tomorrow
    4wks before socm
    4wks
    since socm for 2wks

A tagset is a set of unique UTF-8 strings, each identifying some trackable
entity.

  <tagset>:
    <tag> [<tag> ...]

Examples of a tagset:

    Home                                    (1 tag)
    'Fiscal Policy Alignment Project'       (1 tag)
    Fiscal\ Policy\ Alignment\ Project      (1 tag)
    Home Garden                             (2 tags)

A tag may have any value that is not a supported form of date or duration.


Hints
-----
There are built-in and custom hints, that look like this:

  :fill

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 hints 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
  :week       Macro that means 'this week'
  :debug      Turns on debugging mode
  :x          User defined
  :color      Force use of color on
  :nocolor    Force use of color off
  :yes        Override confirmation
  :ids        Show ephemeral IDs for manipulation

It is not an error to specify extra hints, because they will be simply ignored.
Unrecognized hints yiled warnings.


--- Raw Notes ---

- 'timew import <file>' will merge data.

- A command for a daily and weekly view of exclusions is needed. To verify that
  they are correctly defined. A text-based list should accompany it.

- Use :ids to show the ephemeral IDs, then use 'merge' and 'split' commands to
  combine intervals.  Then:

  $ timew @1 modify ...
  $ timew @1 @2 merge
  $ timew @1 clear