[boost] [modularization] Extracting lexical_cast from conversion

Conversion depends on Math and Range due to lexical_cast. /math/ <http://www.pdimov.com/tmp/report-6d1f271/math.html> |<boost/math/special_functions/fpclassify.hpp>| * from |<boost/lexical_cast.hpp>| |<boost/math/special_functions/sign.hpp>| * from |<boost/lexical_cast.hpp>| /range/ <http://www.pdimov.com/tmp/report-6d1f271/range.html> |<boost/range/iterator_range_core.hpp>| * from |<boost/lexical_cast.hpp>| |Extracting LexicalCast  allows to break these cycle|s Conversion -> Math -> Conversion -> Range -> Conversion Best, Vicente P.S. This dependencies have been introduced lately while trying to make the implementation more efficient.