Upgrade log4j to the latest 2.x version

[TilmanNeumann]

log4j 1.x has several vulnerabilities. Although I don't know if they apply to the simple way I am using the library, it should be upgraded.

[TilmanNeumann]

Today I added a Maven build for an executable jar and worked over the log4j2 configuration initialization. jml now takes the log4j2 configuration specified by the log4j2.configurationFile system property as first choice which should be specially useful when it is embedded into another project as a jar.

That should be all that was still missing.