update maven-assembly-plugin

- use version to 2.4
- build assembly now with command
  mvn package  (assembly:assembly is deprecated)
- adjusted README.md
added UDF to normalize link targets to DBpedia URIs
added macro file that contains functionality of main scripts

will be used by (at least)
- examples/indexing/names_and_entities.pig
- examples/nerd-stats/nerd-stats.pig
scripts import macros

- nerd-stats.pig and names_and_entities.pig both use macros
- deleted examples/indexing/names_and_entities_low_memory.pig