replace limits.h with climits

The former was deprecated with C++14. The standard says they are the same
with one exception:

The header<climits>defines all macros the same as the C standard library
header<limits.h>.

[Note:The types of the constants defined by macros in<climits>are not
required to match the types to which themacros refer.— end note]

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/Main.cxx

@@ -115,7 +115,7 @@
 #include <locale.h>
 #endif
 
-#include <limits.h>
+#include <climits>
 
 static constexpr size_t KILOBYTE = 1024;
 static constexpr size_t MEGABYTE = 1024 * KILOBYTE;