Remove <algorithm> header from the common path

It was only used for std::max<double> within Approx, so we now have
::Catch::Detail::max(double, double) that is used instead.

include/internal/catch_approx.cpp

@@ -13,6 +13,13 @@
 namespace Catch {
 namespace Detail {
 
+    double max(double lhs, double rhs) {
+        if (lhs < rhs) {
+            return rhs;
+        }
+        return lhs;
+    }
+
     Approx::Approx ( double value )
     :   m_epsilon( std::numeric_limits<float>::epsilon()*100 ),
         m_margin( 0.0 ),

include/internal/catch_approx.hpp

@@ -10,7 +10,6 @@
 
 #include "catch_tostring.h"
 
-#include <algorithm>
 #include <cmath>
 
 #include <type_traits>
@@ -18,6 +17,8 @@
 namespace Catch {
 namespace Detail {
 
+    double max(double lhs, double rhs);
+
     class Approx {
     public:
         explicit Approx ( double value );
@@ -42,7 +43,7 @@ namespace Detail {
         friend bool operator == ( const T& lhs, Approx const& rhs ) {
             // Thanks to Richard Harris for his help refining this formula
             auto lhs_v = static_cast<double>(lhs);
-            bool relativeOK = std::fabs(lhs_v - rhs.m_value) < rhs.m_epsilon * (rhs.m_scale + (std::max)(std::fabs(lhs_v), std::fabs(rhs.m_value)));
+            bool relativeOK = std::fabs(lhs_v - rhs.m_value) < rhs.m_epsilon * (rhs.m_scale + (max)(std::fabs(lhs_v), std::fabs(rhs.m_value)));
             if (relativeOK) {
                 return true;
             }