Need to keep up with std::ascii reform

[akosthekiss]

When building cargo with (very) recent rustc, then errors like below are reported:

/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:532:39: 532:49 error: type `char` does not implement any method in scope named `to_ascii`
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:532                     let start = start.to_ascii().to_lowercase();
                                                                                                                            ^~~~~~~~~~
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:533:35: 533:45 error: type `char` does not implement any method in scope named `to_ascii`
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:533                     let end = end.to_ascii().to_lowercase();
                                                                                                                        ^~~~~~~~~~
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:543:35: 543:45 error: type `char` does not implement any method in scope named `to_ascii`
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:543                         let c = c.to_ascii().to_lowercase().as_char();
                                                                                                                        ^~~~~~~~~~
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:566:11: 566:21 error: type `char` does not implement any method in scope named `to_ascii`
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:566         a.to_ascii().to_lowercase() == b.to_ascii().to_lowercase()
                                                                                                ^~~~~~~~~~
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:566:42: 566:52 error: type `char` does not implement any method in scope named `to_ascii`
/home/akiss/.cargo/registry/src/github.com-1ecc6299db9ec823/glob-0.1.1/src/lib.rs:566         a.to_ascii().to_lowercase() == b.to_ascii().to_lowercase()
                                                                                                                               ^~~~~~~~~~

This seems to be the case since rust-lang/rust@070ab63 , and the cause of the error is also present in current HEAD of glob.

(This is very similar to alexcrichton/curl-rust#45 and dtolnay/semver#27 )