Add remaining time estimate to Ninja status.

[jpakkane]

Creates a new token %h (for "human readable", more suitable letters were already taken) that displays an estimate on how long the current build will last.

It's meant to be informative rather than accurate. When there is a lot of time remaining it will look like this:

1h 15m

and when there is only a small amount of work left it looks like this:

53s

[jpakkane]

Does this pull request address historical data from previous builds?

No.

which I don't think is accurate at all.

This MR is not meant to be to be super accurate. It is to give a rough estimate to the user. Simply getting to know whether the build will take 5 seconds, a minute, 5 minutes or 30 minutes is useful on its own. It is better than having no estimates at all, which is the current situation.

Better would be to offer no estimate at all for the first build, and then subsequently offer estimates based on how long each task has taken in the past

That can be done but it will take a lot more code. Doing it right takes on the order of hundreds of lines of code whereas this MR is around 20. Also the exact estimation algorithm can be changed later so if someone wants to improve the accuracy, they can do that later in a separate merge request.

[jhasse]

Closing in favor of #1963.