Rewrite gets in assembler

+19 bytes if used alone, because it pulls in fgets, but as code is
factorized, -128 bytes in programs using both fgets and gets.

test/ref/test_gets.c

@@ -0,0 +1,46 @@
+/*
+  !!DESCRIPTION!! gets test
+  !!LICENCE!!     Public domain
+*/
+
+#include "common.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <ctype.h>
+
+char buf[512];
+
+#define INFILE   "cf.in"
+
+#ifndef __CC65__
+/* Force declaration on host compiler, as gets() is deprecated for
+ * being dangerous as hell */
+char *gets (char *__s);
+#endif
+
+#ifdef NO_OLD_FUNC_DECL
+int main(int argc,char **argv)
+#else
+main(argc, argv)
+int argc;
+char *argv[];
+#endif
+{
+    /* Fake stdin with the reference file */
+    fclose(stdin);
+    stdin = fopen(INFILE, "r");
+    if (stdin == NULL) {
+        return EXIT_FAILURE;
+    }
+
+    while (gets(buf) != NULL)
+    {
+        printf("%s",buf);
+    }
+
+    fclose(stdin);
+    return 0;
+}