Kernel/LibC: add free function for FixedWidthAllocator

I have to rework the syscall API and allocators in process. For
now this works well enough :)

userspace/test.c

@@ -3,42 +3,24 @@
 
 int main()
 {
-	void* ptr = malloc(10);
-	if (ptr == NULL)
+	for (int i = 0; i < 10; i++)
 	{
-		perror("malloc");
-		return 1;
-	}
-	*(int*)ptr = 5;
-	putc('0' + *(int*)ptr, stdout);
-	return 0;
-
-	FILE* fp = fopen("/boot/grub/grub.cfg", "r");
-	if (fp == NULL)
-	{
-		perror("fopen");
-		return 1;
-	}
-
-	for (;;)
-	{
-		char buffer[128];
-		size_t nread = fread(buffer, 1, sizeof(buffer) - 1, fp);
-		if (nread == 0)
+		int* ptrs[10];
+		for (int j = 0; j < 10; j++)
 		{
-			if (ferror(fp))
-				perror("fread");
-			break;
+			ptrs[j] = malloc(10);
+			if (ptrs[j] == NULL)
+			{
+				perror("malloc");
+				return 1;
+			}
+			*ptrs[j] = j;
+			putc('0' + *ptrs[j], stdout);
 		}
-		buffer[nread] = '\0';
-		fputs(buffer, stdout);
+		for (int j = 0; j < 10; j++)
+			free(ptrs[j]);
+		putc('\n', stdout);
 	}
-
-	if (fclose(fp) == EOF)
-	{
-		perror("fclose");
-		return 1;
-	}
-
+	
 	return 0;
 }