Add internal documentation for the new command parsing code

src/main/java/de/prob2/jupyter/CommandUtils.java

src/main/java/de/prob2/jupyter/Parameter.java

src/main/java/de/prob2/jupyter/ParameterBase.java

src/main/java/de/prob2/jupyter/ParameterCompleters.java

src/main/java/de/prob2/jupyter/ParameterInspectors.java

src/main/java/de/prob2/jupyter/Parameters.java

src/main/java/de/prob2/jupyter/ParsedArguments.java

src/main/java/de/prob2/jupyter/PositionedString.java

src/main/java/de/prob2/jupyter/SplitArguments.java

src/main/java/de/prob2/jupyter/SplitResult.java