Add changelog and document breaking changes

[aminya]

0.4 to 0.5 had some breaking changes, which are not documented anywhere.

For example, from_case no longer works on str.

[rutrum]

Hi, breaking changes were not intended, so thank you for bringing this to my attention. I rewrote the trait implementation for Casing. You can see a major change in this commit:

f74aed7#diff-b1a35a68f14e696205874893c07fd24fdb88882b47c23cc0e0c80a30c7d53759

Did from_case every work on str? It currently works on, and did work on &str. Can you give me an example of something that succeeded in 0.4 and fails now? I might be misunderstanding something.

[rutrum]

As I move forward into 0.7.0 I will start documenting changes best I can. I am relying on the "0.x is unreliable" part of semver perhaps a little too heavily, since this library is relatively mature. I may in the future look backwards and try to document the breaking changes between older versions.

As far as your note on str, I am in the process of changing the trait bounds for the Casing trait which should hopefully increase the number of string types case conversion should work upon.