Added String class

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added Bytecodes class

- this is slightly different from what the Java implementation does
- the main reason is that Python does not have a switch/case statement, but this approach here is also more declarative, a little nicer, and less redundant

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added MethodGenerationContext class

Signed-off-by: Stefan Marr <git@stefan-marr.de>