Code cleanups


SetPropSubCommandHandler.java:
Extracted methods parseValue() and getPropertyDefinition().

Argument.java:
Improved the toString() + javadocs.
Minor code cleanups.

ArgumentParser.java:
Removed one parseArguments() method - never used.
Extracted method indentAndWrap() to match SubCommandArgumentParser.
Minor code cleanups.

SubCommandArgumentParser.java:
Removed one parseArguments() method - never used.
Minor code cleanups.

DsconfigOptionsTestCase.java:
Added testGenerateDoc().
Minor code cleanups.