adding a constant mantissamask.hpp and simplifying the impl of mantissa scalar and simd
Merge branch 'master' into simplifying_mantissa

Conflicts:
	modules/boost/simd/base/include/boost/simd/ieee/functions/simd/common/mantissa.hpp
moving an include into guards in mantissa.hpp
bad move of include in mantissa
modyfing ldexp in order it is consistent with ldexp
Merge branch 'master' into correcting_ldexp

Conflicts:
	modules/boost/simd/base/include/boost/simd/ieee/functions/simd/common/mantissa.hpp
corrections according some remarks
corrections according some remarks
modyfing ldexp in order for it to be consistent with frexp