Log the original calling location, rather than the wrapper function

[MinchinWeb]

I've noticed that when Pelican logs warnings and errors, the file number and line number are always the same. It turns out we wrap the calling of warnings and errors (but not other logging levels) to allow warnings to be fatal, etc, but it is thus reporting the location of that wrapper function, rather than the "true" caller.

This isn't as helpful as it could be when trying to understand what is going on under the covers.

This is a small patch that allows the logger to show the "true" caller.

Before:

[20:40:37] WARNING  [Seafoam] Development Mode is active. Image Process has been disabled.                     log.py:94
           WARNING  AUTHOR_URL is set to None                                                                  log.py:94
Done: Processed 4 articles, 0 drafts, 0 hidden articles, 0 pages, 0 hidden pages and 0 draft pages in 0.51 seconds.

After:

[20:51:24] WARNING  [Seafoam] Development Mode is active. Image Process has been disabled.              initialize.py:51
           WARNING  AUTHOR_URL is set to None                                                         urlwrappers.py:116
Done: Processed 4 articles, 0 drafts, 0 hidden articles, 0 pages, 0 hidden pages and 0 draft pages in 0.48 seconds.

The required feature was added in Python 3.8.
c.f. https://stackoverflow.com/a/55998744/4276230

[MinchinWeb]

This would fix #3037. C.f. #3038.

[boxydog]

Cool.

[justinmayer]

@MinchinWeb: Many thanks for this fix! 👏