c0d0e68be4
exclusive range patterns
adds `..` patterns to the language under a feature gate (`exclusive_range_pattern`).
This allows turning
``` rust
match i {
0...9 => {},
10...19 => {},
20...29 => {},
_ => {}
}
```
into
``` rust
match i {
0..10 => {},
10..20 => {},
20..30 => {},
_ => {}
}
```