improved pretty printer

src/main/java/de/tla2b/TLA2B.java

src/main/java/de/tla2b/output/ASTPrettyPrinter.java

src/main/java/de/tla2b/output/Indentation.java

src/main/java/de/tla2bAst/BAstCreator.java

src/test/java/de/tla2b/prettyprintb/ExampleFilesTest.java

src/test/java/de/tla2b/prettyprintb/SetsTest.java

src/test/java/de/tla2b/prettyprintb/TupleTest.java

src/test/java/de/tla2b/util/TestUtil.java