More scanners

[DanielKeep]

Ideas for more scanners.

Self scanners:

• std::path::Path[Buf] - Path would probably only work on paths without spaces in them. You could also quote them, but that would only work for PathBuf. One other edge case is handling path separators for the current platform (for parsing PATH). There's enough variance that it might be simpler to just require the use of an abstract scanner. - decided that there isn't enough benefit here over just using a regular string scanner of some description. Once Rustc confuses lifetimes of different unrelated variables of type &'static str when implementing a trait for &'a str rust-lang/rust#26448 gets fixed, they should all just work for paths, anyway.

Abstract scanners:

• Various for std::time::Duration - Duration doesn't have a very nice Debug representation (although it could be parsed). Would probably be nicer to just have scanners for various units of time (Seconds, Days, etc.). ISO 8601 is a bit ugly, but covers all the usual bases. If there's demand, shorthand f64 -> Duration scanners can be added.
• HorizontalSpace - match any horizontal spaces: \x20, \t, etc., but not newlines or vertical tabs.
• Newline - match any of \r, \r\n, \n.

Runtime scanners:

• until(impl Pattern) - slice until a given std::str::pattern::Pattern matches.
• pat(impl Pattern) - use str::starts_with. - impossible given current Pattern design.

[DanielKeep]

Fixed in b492961.