log_first_n implementation doesn't match doc, ignores formatting args

[glados-verma]

The log_first_n doc says:

Logs 'msg % args' at level 'level' only first 'n' times

However, the implementation only tracks the caller's file and line number, and ignores the formatting args. So if I do something like:

for arg in ['arg1', 'arg2']:
  log_first_n('%s', 1, arg)

It will never log for arg2.

[yilei]

I can see how the docs can be interpreted as such. The implementation is the intention here, it only logs N times regardless what the message is.

Keeping this open so we'll remember to clarify it. Or feel free to send a PR.