Removed doc comments because rustdoc is stupid.
Removed NegInt scanner.
Simplified int scanner.
Added tests for int scanner.
Created ScanCursor trait to simplify scanners.

Instead of needing to parameterise on everything Cursor does, a scanner
now only needs `'a` and `Cur: ScanCursor<'a>`.
Removed scanned_value business.

I'll just wait for UFCS.
Removed unused import.
Added uint scanner.

Also moved the FromStr use out to module level.
Replaced int and uint scanners with macros.
Added sized int scanners and an example.
Added bool scanner.
Added f32 and f64 scanners.
Modified Scanner trait to have lifetime parameter.

Required for zero-copy &str scanning.
Added &str scanner.
Added char scanner.
Added gen for alts and reps.

Lots of changes.  Too lazy to split them up.
Removed redundant type parameter on Scanner.