constexpr -> SBE_CONSTEXPR (#793)
constexpr -> SBE_CONSTEXPR (#793)

* constexpr -> SBE_CONSTEXPR

* Fixes warning
warning C4267: 'argument' : conversion from 'size_t' to 'const uint16_t', possible loss of data
real-logic/simple-binary-encoding,real-logic/simple-binary-encoding,real-logic/simple-binary-encoding,PKRoma/simple-binary-encoding,PKRoma/simple-binary-encoding,PKRoma/simple-binary-encoding,real-logic/simple-binary-encoding,PKRoma/simple-binary-encoding,real-logic/simple-binary-encoding,PKRoma/simple-binary-encoding,PKRoma/simple-binary-encoding,real-logic/simple-binary-encoding,real-logic/simple-binary-encoding,PKRoma/simple-binary-encoding