feat: implemented errno, strtol. Started ustar. Reformatted headers and

code. Added some self-tests. Started prepwork for vfs.

kernel/libc/string.c

@@ -20,7 +20,7 @@ int memset(void *dst, int data, size_t amount) {
 }
 
 
-int strcpy(char *dst, char *src) {
+int strcpy(char *dst, const char *src) {
     return memcpy(dst, src, strlen(src) + 1);
 }