Makes all children modules use parent pom

Hey,

To simplify releases and configuration, I've made all child modules inherit from the parent pom. I've also moved common configuration (such as sourceEncoding) to the parent, since this is now inherited by the children. Moreover, the parent pom inherits from sonatype oss to get distributionManagement tags etc.

I have *not* done any pluginManagement or dependencyManagement stuff. But at least now its possible to do so (to enforce e.g. the same version of slf4j-api in all artifacts).

Have a look and see what you think. Once this has been merged, I will try to merge master into 0.3.x and perform a 0.3.1 release.