Dependency on gsl-lite removed as it causes issues with compiler-explorer

src/include/units/bits/hacks.h

@@ -23,6 +23,10 @@
 #pragma once
 
 #include <experimental/ranges/concepts>
+#include <exception>
+
+
+#define Expects(cond) if(!(cond)) ::std::terminate();
 
 namespace std {
 

src/include/units/quantity.h

@@ -25,7 +25,6 @@
 #include <units/unit.h>
 #include <units/bits/concepts.h>
 #include <limits>
-#include <gsl/gsl-lite.hpp>
 
 namespace std::experimental::units {
 

src/include/units/ratio.h

@@ -22,10 +22,10 @@
 
 #pragma once
 
+#include <units/bits/hacks.h>
 #include <type_traits>
 #include <numeric>
 #include <cstdint>
-#include <gsl/gsl-lite.hpp>
 
 namespace std::experimental::units {