kernel: various changes.

+ kernel: replace sk-hello test executable with a test initramfs
+ panic: start implementing a proper kernel panic screen
+ lib: added a new string.h library for string manipulation.
+ kernel: replace all the strlen implementations with the strlen() function

kernel/src/lib/string.c

@@ -0,0 +1,57 @@
+#include <lib/string.h>
+#include <stddef.h>
+
+int strlen(const char *str) {
+  int len = 0;
+  while (str[len])
+    len++;
+  return len;
+}
+
+int strcmp(const char *s1, const char *s2) {
+  while (*s1 && *s1 == *s2) {
+    s1++;
+    s2++;
+  }
+  return *s1 - *s2;
+}
+
+char *strcpy(char *dest, const char *src)
+{
+    if (dest == NULL || src == NULL)
+        return NULL;
+    
+    char *temp = dest;
+    while((*dest++ = *src++) != '\0'); 
+    return temp;
+}
+
+char *strchr(const char *s, int c) {
+  while (*s++) {
+    if (*s == c)
+      return (char *)s;
+  }
+  return NULL;
+}
+
+char *strrchr(const char *s, int c) {
+    const char *p = NULL;
+
+    for (;;) {
+        if (*s == (char)c)
+            p = s;
+        if (*s++ == '\0')
+            return (char *)p;
+    }
+}
+
+int oct2bin(unsigned char *str, int size) {
+    int n = 0;
+    unsigned char *c = str;
+    while (size-- > 0) {
+        n *= 8;
+        n += *c - '0';
+        c++;
+    }
+    return n;
+}

kernel/src/lib/string.h

@@ -0,0 +1,8 @@
+#pragma once
+
+int strlen(const char *str);
+int strcmp(const char *s1, const char *s2);
+char *strchr(const char *s, int c);
+char *strcpy(char *dest, const char *src);
+char *strrchr(const char *s, int c);
+int oct2bin(unsigned char *str, int size);