Document RFC 0879 (small-base-lexing) and RFC 0463 (future-proof-literal-suffixes)

[alercah]

RFC 0879
[RFC 0463](https://github.com/rust-lang/rfcs/blob/master/text/0463-future-proof-literal-suffixes.md

[alercah]

Our grammar in https://doc.rust-lang.org/nightly/reference/tokens.html#number-literals currently does not document that octal and binary literals are lexed with all decimal digits; it should do so and then remark in the prose that such literals are lexed as one token but are semantically invalid.

[alercah]

Added RFC 0463 since it's in the same place and serves a similar purpose.

[kubycsolutions]

Just checking my understanding: You're saying that the lexer sees 0b110127 as a malformed token rather than a BIN_LITERAL immediately followed by a DEC_LITERAL as the documentation suggests it should?

If so, are you sure you want to change the doc rather than the lexer?

[mattheww]

The current documentation is correct for numeric literals (and what it says is that 0b110127 is a reserved form).

This issue is still open because suffixes on string literals aren't completely documented.