LGTM: [skip ci]: Ambiguously signed bit-field member

Until C++11 bit fields with integral types should have explicit signedness only.
It is implementation specific whether an -typed bit field is signed, so there could be unexpected sign extension or overflow.

This means that if depending on the compiler int32_t is not explicitly defined as signed the UnitSignature structure may not work
as expected. Since C++14 this has changed and an int of a bit-field is always signed:
https://stackoverflow.com/questions/33723631/signed-bit-field-in-c14

src/Base/Unit.h

@@ -43,6 +43,9 @@ namespace Base {
 #define UnitSignatureLuminousIntensityBits 4
 #define UnitSignatureAngleBits 4
 
+// Hint:
+// https://en.cppreference.com/w/cpp/language/bit_field
+// https://stackoverflow.com/questions/33723631/signed-bit-field-in-c14
 struct UnitSignature{
     int32_t Length:UnitSignatureLengthBits;
     int32_t Mass:UnitSignatureMassBits;