De-duplication using macros

There is a lot of duplicated Pig Latin code in `nerd-stats.pig`, `names_and_entities.pig`, `names_and_entities_low_memory.pig` and some more.

This PR introduces macros to de-duplicate, along with a UDF to normalize URIs.

`names_and_entities_low_memory.pig` is deleted for now. [Line 35 or 36](https://github.com/maxjakob/pignlproc/blob/61badf02d08e7c1df12d53081106d43b0ba55038/examples/indexing/names_and_entities.pig#L35) in `names_and_entities.pig` can be commented out/in. We could bring the separate script back if needed.

Also updates maven-assembly-plugin.

Fixes #5.