Provide optional monospace PR comment layout

[EnricoMi]

In #26 we have discussed how a monospace comment could look like. Here is a suggestion:

521 suites (-60) in 4h 24m 19s (-5m 23s)
508 tests (+1) 482 success (+1) 26 skipped (±0) 0 failed (±0)	9 876 runs (-1 190) 7 873 success (- 896) 2 003 skipped (- 294) 0 failed (± 0)
results for commit e826078 ± comparison against base commit 3fefb1a

and without runs:

521 suites (-60) in 4h 24m 19s (-5m 23s)

508 tests (+1) 482 success (+1) 26 skipped (±0) 0 failed (±0)

results for commit e826078 ± comparison against base commit 3fefb1a

Implement that as an optional comment layout.

[Fox32]

This idea looks great, looking forward to it! I also like your thoughts on the thousands separator in the PR, space should be the least confusing one.