Add "{status}" placeholder

[jwodder]

Closes #20.

[yarikoptic]

Looks great, thank you. But let's add a safe-guard

[yarikoptic]

Just realized an ambiguity -- this the status for the entire "build" (which could have multiple jobs/workflows).
Could there also be the one per each individual job, smth like {job_status}?

I am ok to merge as is, if you do not see a conflict/ambiguity to resolve while in this PR.

[jwodder]

@yarikoptic The statuses are for whatever's logs gets saved at the path. For GitHub, this is the workflow run status. For Travis and Appveyor, this is the job status.

[yarikoptic]

ah, gotcha... confirmed with looking at

$> ls -ld pr/*/*/*/*-*/                                                                  
drwx------ 1 yoh yoh  40 Apr 27 12:29 pr/5539/def0f2aa6673c2291b982bccb2502cea1787bc16/appveyor/5874-failed//
drwx------ 1 yoh yoh 400 Apr 27 12:29 pr/5539/def0f2aa6673c2291b982bccb2502cea1787bc16/appveyor/5874-success//

in my config where I assumed it to be for a build I ended up with groupping of failed-vs-success for the same build in different directories. ok, let's proceed for now -- not yet sure if I really need the "build status"