Add traits IntoAscii* to replace (Owned)AsciiCast

[tormol]

AsciiCast has un-rustic names, and doesn't work well for Ascii (see first commit)

Another issue is that the traits aren't implemented for their target type,which breaks the pattern fn foo<B:Into<Bar>>(b: B).
Hopefully AsciiExt gets stabilized soon.
(Then this could be used by AsciiString.push())

IntoAsciiStr / The third commit is unfinished, just cherry-pick the first two if I don't finish it.

I haven't removed changed anything, so this is not a breaking change. The idea is to make a minor release, and then remove (Owned)AsciiCast, Ascii::from_byte() and more later.

[tormol]

Why do you test on 1.1?

I split this and #18 into two pulls because I thought they were independent, But #18 would help in writing tests.
And some of the methods in Into(Mut)AsciiStr are complex enough to really need testing.

When you merge that I'll write those, rebase and squash some of the commits.

[tormol]

Rebased and:

Prepended two semi-related commits because I didn't bother creating new pull requests.

In ascii_str:

• Replaced Into with As in the conversion traits since they are basically failable As{Ref,Mut}.
  What do you think?
• Added methods to the error struct.
• Removed .ascii_part():
  Name didn't fit in with the other methods, and it can be replaced with s.into_ascii().map_err(|err| s[..err.index()].as_ascii().unwrap() ).
• Wrote tests and fixed bug.

I thought about adding a method to AsAsciiStrError to return u8 or char, but there are enough types already. Most users will know whether they called .as_ascii() on an [u8] or str, but by making .char() return an option instead of panicing, generic converters can figure it out if they somehow want to.

[tomprogrammer]

This crate is tested on 1.1 to detect unintended breaking changes, because raising the compilers version is technically a breaking change. That said I don't think it isn't much of a problem to intentionally raise the version, if we test with that particular version. I will check breaking updates using the reverse dependencies feature crates.io provides.

I will cherry pick the commit "Implement Default, From<&mut[Ascii]> and As{Ref,Mut}<[Ascii]> for AsciiStr". Thanks!

I like the names AsAsciiStr and AsMutAsciiStr, they reflect the names of the infallible conversion traits in std::convert. I'm also fine with removing .ascii_part(), we instead may want to introduce lossy conversions, which are infallible. Lossy conversions are stuff for another PR since there arise some questions how to implement and document them to reduce confusion among users.

It's a bit unfortunate that even IntoAscii exists, maybe we can unify it with IntoAsciiString, since Ascii is inherently owned?

Thanks for your work and sorry for the delay I caused!

[tormol]

Unifying traits would require an associated type, so <T: IntoAsciiString> becomes <T: IntoAscii<Target=AsciiString> which is quite a bit longer.
I can't see when one would want to be generic over Ascii and AsciiString either.

The library still builds on 1.1 (and travis still checks that), It's only the tests that doesn't.
As long as we or rust don't introduce silent breaking changes, shouldn't tests passing on later versions be valid for 1.1?
Must dev-dependencies follow semver?

In about a month AsciiExt will become available on stable. Then I think we should remove the unstable feature and make 1.9 the minimum. I have created a branch where I've started removing the old traits.

[tormol]

Rebased and changed a few things:

• Squashed the travis changes into Add AsAsciiStr.
• Added some blank lines here and there.
• Rewrote documentation.

[tomprogrammer]

Since these traits are mainly used for generic conversions I agree we should keep them separate. Four traits isn't too much, I'm simply over-engineering. ;)

I think skipping 1.1 for the tests is ok. What is the minimal required version for the tests? Maybe we want to increase the minimum rustc version that is guaranteed to work, advertising that earlier versions may work but are not tested. I have some changes in my queue that require rustc 1.3.

Mh, in my opinion dev-dependencies also must follow semver like normal dependencies do. The crate author doesn't know as which kind of dependency another programmer will use it.

I agree, great that AsciiExt is going to be stabilized.

This branch seems ready to merge, are you polishing the last bits and pieces or can I merge?

[tormol]

I'm finished.