Log checkpoints

A checkpoint is a kind of marker in time. It allows to easily reference the associated point in time by just giving its name.

Here is a sample workflow:

$ walt log add-checkpoint exp1-start
[... run experience exp1 ...]
$ walt log add-checkpoint exp1-end
$ walt log show --history exp1-start:exp1-end > exp1.log

By using walt log add-checkpoint with option --date, you can also create a checkpoint referencing a given date. For example:

$ walt log add-checkpoint --date '2015-09-28 15:16:39' some-date-in-2015
$ walt log add-checkpoint --date '-5d' five-days-ago
$ walt log add-checkpoint --date '-2h' two-hours-ago
$ walt log add-checkpoint --date '-3m' three-minutes-ago
$ walt log add-checkpoint --date '-30s' thirty-seconds-ago

For the sake of completeness, commands walt log list-checkpoints and walt log remove-checkpoint are also provided, and their use should be obvious.