Windows instructions updated

Hi,

Perl on Windows got quite a bit easier in the last 10 years. You can now simply install log4perl with your cpan client, just as on Linux or OS X, and also the Windows perl distributions do come with a compiler.

The instructions of log4perl still point at a PPM directory that has not been updated since 2003 and contains an out-of-date version of log4perl. Apart from that, the log4perl ppm is now available in the ActiveState repositories as well.

With this pull request I simplify and correct the docs in this regard. Also I fixed some (minor) POD errors, of which some generated display issues.