refactor parsers and composers

alib2/src/alphabet/SymbolFeatures.h

alib2/src/alphabet/SymbolFromStringParser.cpp

alib2/src/alphabet/SymbolFromStringParser.h

alib2/src/alphabet/SymbolFromXMLParser.cpp

alib2/src/alphabet/SymbolFromXMLParser.h

alib2/src/automaton/AutomatonFromXMLParser.cpp

alib2/src/automaton/AutomatonFromXMLParser.h

alib2/src/factory/AutomatonFactory.cpp

alib2/src/factory/LabelFactory.cpp

alib2/src/factory/RegExpFactory.cpp

alib2/src/factory/StringFactory.cpp

alib2/src/factory/SymbolFactory.cpp

alib2/src/label/LabelFeatures.h

alib2/src/label/LabelFromStringParser.cpp

alib2/src/label/LabelFromStringParser.h

alib2/src/label/LabelFromXMLParser.cpp

alib2/src/label/LabelFromXMLParser.h

alib2/src/regexp/RegExpFromStringParser.cpp

alib2/src/regexp/RegExpFromStringParser.h

alib2/src/regexp/RegExpFromXMLParser.cpp