type inference on all registration variables

alib2raw/src/string/StringToRawComposer.cpp

alib2raw/src/tree/TreeToRawComposer.cpp

alib2str/src/alphabet/SymbolToStringComposer.cpp

alib2str/src/automaton/AutomatonToStringComposer.cpp

alib2str/src/grammar/GrammarToStringComposer.cpp

alib2str/src/label/LabelToStringComposer.cpp

alib2str/src/primitive/PrimitiveToStringComposer.cpp

alib2str/src/string/StringToStringComposer.cpp

alib2str/src/tree/TreeToStringComposer.cpp

alib2str_experimental/src/graph/GraphToStringComposer.cpp