reimplement from/to string parsers/composers

aconvert2/src/DotConverter.cpp

aconvert2/src/GasTexConverter.cpp

aconvert2/src/aconvert.cpp

alib2algo/test-src/grammar/simplify/GrammarToCNFTest.cpp

alib2algo/test-src/regexp/RegExpTest.cpp

alib2algo/test-src/regexp/properties/RegExpEmptyTest.cpp

alib2algo/test-src/regexp/properties/RegExpEpsilonTest.cpp

alib2algo/test-src/regexp/simplify/RegExpOptimizeTest.cpp

alib2algo/test-src/regexp/toAutomaton/re2faTest.cpp

...2algo/test-src/regexp/transform/RegExpConcatenateTest.cpp

alib2algo/test-src/regexp/transform/RegExpDerivationTest.cpp

alib2algo/test-src/regexp/transform/RegExpIntegralTest.cpp

alib2data/src/FromStringParser.hpp

alib2data/src/StringApi.cpp

alib2data/src/StringApi.hpp

alib2data/src/alphabet/SymbolFromStringLexer.cpp

alib2data/src/alphabet/SymbolFromStringLexer.h

alib2data/src/alphabet/SymbolFromStringParser.cpp

alib2data/src/alphabet/SymbolFromStringParser.h

alib2data/src/alphabet/SymbolToStringComposer.cpp