This PR adds and updates docstrings for syntax (and one for ranges).
The reference manual's section on syntax operators is gaining more
content, so the resulting docstrings were reviewed and the missing ones
added.
This PR renames `Substring` to `Substring.Raw`.
This is to signify its status as a second-class citizen (not deprecated,
but no real plans for verification, like `String.Pos.Raw`) and to free
up the name `Substring` for a possible future type `String.Substring :
String -> Type` so that `s.Substring` is the type of substrings of `s`.
The functions `String.toSubstring` and `String.toSubstring'` will remain
for now for bootstrapping reasons.
This PR renames `String.endPos` to `String.rawEndPos`, as in a future
release the name `String.endPos` will be taken by the function that is
currently called `String.endValidPos`.
This PR fixes `getHexNumSize` to consider underscores. Previously, only
the amount of bytes was counted, making it output 9 for `1234_abcd`
instead of the actual number of digits, which is 8.
This PR adds a new helper parser for implementing parsers that contain
hexadecimal numbers. We are going to use it to implement anchors in the
`grind` interactive mode.
