C23 features

[nagbu1]

Hey Beej! There are a couple of C23 changes you probably want to mention

• 14.5.1.1. Notes on binary Your prediction came true! C23 has now binary expressions with 0b. The text needs to be updated to reflect this.
• 5.5 The NULL pointer In C23 you want to use the nullptr constant instead of NULL.

I haven't finished reading through the text yet. Though I'm not an expert on C23, I will keep an eye out for these changes.

---

I use GitHub under protest

[cfr42]

Somebody told me constexpr should now be used rather than #define, but it is hard to find any information about this, so I was wondering if you might be willing to add something when you have time.

[Note that I know almost no C at this point, so if the above makes no sense, that is probably why.]