Add fletcher16-gen developer util

1. I'm not convinced our fletcher16 implementation is proper
2. It is not in coreutils

So we add some basic code to do that.

This is also the first dev-util, so add some documentation to DEVEL.md.

dev-utils/m2-functions/string.c

@@ -0,0 +1,59 @@
+/*
+ * SPDX-FileCopyrightText: 2016 Jeremiah Orians
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include<stdlib.h>
+#include<stdio.h>
+#define MAX_STRING 4096
+//CONSTANT MAX_STRING 4096
+// void* calloc(int count, int size);
+void file_print(char* s, FILE* f);
+
+char* copy_string(char* target, char* source)
+{
+	while(0 != source[0])
+	{
+		target[0] = source[0];
+		target = target + 1;
+		source = source + 1;
+	}
+	return target;
+}
+
+char* postpend_char(char* s, char a)
+{
+	char* ret = calloc(MAX_STRING, sizeof(char));
+	if(NULL == ret) return NULL;
+
+	char* hold = copy_string(ret, s);
+	hold[0] = a;
+	return ret;
+}
+
+char* prepend_char(char a, char* s)
+{
+	char* ret = calloc(MAX_STRING, sizeof(char));
+	if(NULL == ret) return NULL;
+
+	ret[0] = a;
+	copy_string((ret+1), s);
+	return ret;
+}
+
+char* prepend_string(char* add, char* base)
+{
+	char* ret = calloc(MAX_STRING, sizeof(char));
+	if(NULL == ret) return NULL;
+
+	copy_string(copy_string(ret, add), base);
+	return ret;
+}
+
+int string_length(char* a)
+{
+	int i = 0;
+	while(0 != a[i]) i = i + 1;
+	return i;
+}