feature: add a few helpers fn (is...)

fix: print unprintable characters no longer occurs

libbozo/headers/ctype.h

@@ -1,11 +1,11 @@
 #pragma once
 
 /*
-int isalnum(int c);
-int isalpha(int c);
 int iscntrl(int c);
 */
 int isdigit(int c);
+int isalpha(int c);
+int isalnum(int c);
 /*
 int isgraph(int c);
 int islower(int c);

libbozo/src/ctype/isalnum.c

@@ -0,0 +1,6 @@
+#include "ctype.h"
+
+int isalnum(int c)
+{
+	return isalpha(c) || isdigit(c);
+}

libbozo/src/ctype/isalpha.c

@@ -0,0 +1,4 @@
+int isalpha(int c)
+{
+	return ('Z' >= c && c >= 'A') || ('z' >= c && c >= 'a');
+}