Document peg grammar: 0

[iacore]

reference: https://github.com/janet-lang/janet/pull/1187#issuecomment-1586490024

[sogaiu]

For comparison, the following is what janet-pegdoc says about integer peg special patterns:

$ pdoc -d integer

`<n>` -- where <n> is an integer

For n >= 0, try to match n characters, and if successful, advance that many characters.

For n < 0, matches only if there aren't |n| characters, and do not advance.

For example, -1 will match the end of a string because the length of the empty string is 0, which is less than 1 (i.e. |-1| = 1 and there aren't 
that many characters).

[iacore]

I changed the wording a bit. It still reads awkward but the meaning is clear.

[sogaiu]

I think that this line:

For example, -1 will match the end of a string.

should come right after this line:

If negative, matches if not that many characters and does not advance.

because -1 is an example of a negative number, while 0 is not.

I think it would be fine to address the case of 0 as the last line (or before the text having to do with negative integers), for example:

0 counts as a match but there is no advancing.

[iacore]

I changed the wording again

[sogaiu]

The latest looks much improved to me :)