Replace Vec<Ascii> and [Ascii] with newtypes

[tomprogrammer]

The ascii crate now provides types for owned ascii strings and borrowed
ascii slices. Their implementation should allow them to be used like
String and str.

Changes:

• AsciiString replaces Vec<Ascii>
• AsciiStr replaces [Ascii]
• Remove Ascii::to_lowercase() and Ascii::to_uppercase()
• Remove traits IntoString, IntoBytes and AsciiStr

Migration (for details see new implementations):

• You can't construct AsciiString and AsciiStr like a collection
  anymore, use the from_bytes or from_str method instead.
• FromStr::from_str for AsciiString and AsciiStr::from_str for
  construction from string slices.
• To convert from the ascii types to bytes or strings please use the
  new generic conversion traits Into and AsRef instead of IntoString, IntoBytes or AsciiStr.
• Use AsciiExt::to_ascii_lowercase() and AsciiExt::to_ascii_uppercase() instead of the removed methods which where implemented directly on Ascii.
• The AsciiCast and OwnedAsciiCast traits are unchanged for now.

New implementations:

• AsciiString::from_bytes and AsciiStr::from_bytes for construction from
  types which can be represented as a byte slice.
• Implements fmt::{Debug, Display} like String does
• AsciiString derefs to AsciiStr, additionally DerefMut is implemented so
  AsciiExt is fully useable
• Implements Hash, Borrow and ToOwned so it can easily be used in
  collections.
• Implements PartialEq, PartialOrd, Eq and Ord for itself and
  str
• AsciiString implements Into<String>, Into<Vec<u8>> and
  AsRef<AsciiStr>
• AsciiStr implements AsRef<[u8]> and AsRef<str>

[breaking-change]

Fixes: #5

As of now documentation and more tests for the new functionality are missing.

[tomprogrammer]

I don't know if I missed to implement important traits. Due to the missing tests I'm not sure if everything works as it should.

@frewsxcv Do you want to test this in your code for feedback?

[frewsxcv]

So I'm a little confused, why did all of this stuff get changed?

[tomprogrammer]

I planned to replace Vec<Ascii> and [Ascii] with custom types some time ago because it was not possible to impl fmt::Debug for Vec<Ascii> in a custom way, due to conflicting generic impl's in std::collections.

Now the new coherence rules also made it difficult to do something like impl AsciiExt for Vec<Ascii> because Vec<Ascii> is not considered a crate local type. Custom crate local types are an easy way to solve this. Custom ascii types do have the advantage, that they can be used like String/str so it's easier to use them. There is another set of types following this: OsString/OsStr

The new generic conversation traits just replaced some specialized traits in this library, similar to what happened in std. I just found some traits I want to implement additionally like FromIterator, Extend and so on.

[frewsxcv]

Can't you use derive(PartialEq) for this?

[tomprogrammer]

Yes, also Eq, PartialOrd, Ord and Hash can be derived on AsciiString. On AsciiStr only Hash can be derived because of rust-lang/rust#23649.

[frewsxcv]

Looks alright with me

[frewsxcv]

@tomprogrammer Need any help with getting the tests to pass?

[tomprogrammer]

@frewsxcv Yes, that would be great. I can't work on it at the moment, exams want to be done.

I learned that the types PartialEq is implemented for must match, there is no auto-dereference. That confused me at beginning.

[tomprogrammer]

I've decided not to throw away Ascii::to_lowercase() and Ascii::to_uppercase() because AsciiExt isn't stable in beta 1.0 yet. Actually this preserves the functionality if we ship a beta 1.0 compatible build of this crate.

[SimonSapin]

Hum, AsciiExt and AsciiExt::to_*case are stable. It’s OwnedAsciiExt that’s not, because it’s meant to be replaced by AsciiExt::make_*case but that requires String to implement DerefMut to be useful. (AsciiExt::make_* take &mut str)

[tomprogrammer]

oh, that is correct. I screwed something up in my head.

Sorry for the frequent breakage, I update ascii again.