Consolidate code for getting platform details into one place (#311)

Consolidate code for getting platform details into a single place

platform.hpp

@@ -0,0 +1,16 @@
+#ifndef PLATFORM_HPP
+#define PLATFORM_HPP
+
+#include <cstddef>
+
+long get_num_avail_cpus();
+
+long get_page_size();
+
+size_t calc_memsize();
+
+size_t get_max_open_files();
+
+constexpr const char *get_null_device() { return "/dev/null"; }
+
+#endif // PLATFORM_HPP