implemented expression translator

src/main/java/de/tla2b/analysis/SpecAnalyser.java

src/main/java/de/tla2b/old/AbstractExpressionPrinter.java

src/main/java/de/tla2b/old/BMachinePrinter.java

src/main/java/de/tla2b/old/DContext.java

src/main/java/de/tla2b/old/ExprReturn.java

src/main/java/de/tla2b/old/ExpressionPrinter.java

src/main/java/de/tla2b/old/ExpressionTranslatorOld.java

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

src/main/java/de/tla2b/old/Tla2BTranslator.java

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

src/main/java/de/tla2b/translation/BMacroHandler.java

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

src/main/java/de/tla2bAst/ExpressionTranslator.java

src/main/java/de/tla2bAst/Translator.java

src/test/java/de/tla2b/expression/SimpleExpressionTest.java

src/test/java/de/tla2b/expression/TestComplexExpression.java

src/test/java/de/tla2b/expression/TestError.java

src/test/java/de/tla2b/expression/TestKeywords.java

src/test/java/de/tla2b/expression/TestSequences.java

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