move src dir to cli and add it's own cmake file.

cli/isatty.cpp

@@ -0,0 +1,21 @@
+#if _WIN32
+#include <io.h>
+#else
+#include <unistd.h>
+#define _isatty isatty
+#define _fileno fileno
+#endif
+#include "isatty.h"
+
+namespace eoskeygen {
+
+bool isatty(int fd) {
+    return ::_isatty(fd);
+}
+
+bool isatty(FILE* fd) {
+	// fileno() segfaults if fd is null.
+    return fd ? isatty(_fileno(fd)) : false;
+}
+
+} // namespace eoskeygen