literals namespace made inline

src/include/units/si/frequency.h

@@ -54,9 +54,7 @@ namespace units {
   template<typename T>
   concept bool Frequency =  Quantity<T> && std::experimental::ranges::Same<typename T::dimension, dimension_frequency>;
 
-  // ...
-
-  namespace literals {
+  inline namespace literals {
 
     // mHz
     constexpr auto operator""_mHz(unsigned long long l) { return frequency<millihertz, std::int64_t>(l); }

src/include/units/si/length.h

@@ -64,7 +64,7 @@ namespace units {
   template<typename T>
   concept bool Length = Quantity<T> && std::experimental::ranges::Same<typename T::dimension, dimension_length>;
 
-  namespace literals {
+  inline namespace literals {
 
     // mm
     constexpr auto operator""_mm(unsigned long long l) { return length<millimeter, std::int64_t>(l); }

src/include/units/si/time.h

@@ -55,9 +55,7 @@ namespace units {
   template<typename T>
   concept bool Time = Quantity<T> && std::experimental::ranges::Same<typename T::dimension, dimension_time>;
 
-  // ...
-
-  namespace literals {
+  inline namespace literals {
 
     // ns
     constexpr auto operator""_ns(unsigned long long l) { return time<nanosecond, std::int64_t>(l); }

src/include/units/si/velocity.h

@@ -46,9 +46,7 @@ namespace units {
   template<typename T>
   concept bool Velocity = Quantity<T> && std::experimental::ranges::Same<typename T::dimension, dimension_velocity>;
 
-  // ...
-
-  namespace literals {
+  inline namespace literals {
 
     // mps
     constexpr auto operator""_mps(unsigned long long l) { return velocity<meter_per_second, std::int64_t>(l); }