Audit Plugin packaging

Currently only .so binaries are provided for the Audit Plugin. Also the filename is purely server_audit.so. The filename doesn't include the version number, which actually is good, because otherwise users would have to change my.cnf every time they want to upgrade to a new version of the Audit Plugin.

To solve this problematic situation of not actually knowing the version number when looking at the files the minimum to do is to create a tarball that in its filename tells the version number, like this:
mariadb-audit-plugin-1.0.0.tar.gz (with the correct version number of course)

The tarball should include the following directories with the corresponding .so files in each directory:
linux-32
linux-32_debug
linux-64
linux-64_debug

Once Windows binaries are being produced a .zip file should be created in a similar fashion.

And once changelogs are being produced they should be added to the tarball and zip.