introduce structure class for regexps

alib2algo/src/automaton/convert/ToRegExpAlgebraic.cpp

alib2algo/src/automaton/convert/ToRegExpStateElimination.cpp

alib2algo/src/equations/LeftRegularEquationSolver.cpp

alib2algo/src/equations/RightRegularEquationSolver.cpp

alib2algo/src/regexp/convert/ToAutomatonThompson.cpp

alib2algo/src/regexp/generate/RandomRegExpFactory.cpp

alib2algo/src/regexp/glushkov/GlushkovTraversal.cpp

alib2algo/src/regexp/properties/RegExpEmpty.cpp

alib2algo/src/regexp/properties/RegExpEpsilon.cpp

alib2algo/src/regexp/simplify/RegExpOptimize.cpp

alib2algo/src/regexp/transform/RegExpAlternate.cpp

alib2algo/src/regexp/transform/RegExpConcatenate.cpp

alib2algo/src/regexp/transform/RegExpDerivation.cpp

alib2algo/src/regexp/transform/RegExpIntegral.cpp

alib2algo/src/regexp/transform/RegExpIterate.cpp

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

alib2data/src/regexp/RegExp.cpp

alib2data/src/regexp/RegExpFeatures.h

alib2data/src/regexp/formal/FormalRegExp.cpp

alib2data/src/regexp/formal/FormalRegExp.h