Add an error type to FromStr impls

[nivkner]

Fixes #119

[alexcrichton]

Awesome, thanks @nivkner! I think in light of #142 though we may wish to remove the Log prefix here perhaps?

@sfackler do you have thoughts on how to manage breaking changes like this? Do you think we should hold off on merging or maybe merge to a separate branch?

[dtolnay]

I would merge to master along with a note in Cargo.toml.

publish = false # this branch contains breaking changes

[nivkner]

Removed the Log prefix as requested.

[alexcrichton]

Thanks @nivkner! We'll take it from here and figure out the best way to land this with other breaking changes to the log crate.

[sfackler]

Seems fine to merge to master - we can always cut an 0.3.x branch if we need more releases from that version.

[dtolnay]

@nivkner any reason these messages are slightly different? I would prefer to pick one or the other.

[dtolnay]

Ah, this matches all of the existing error messages. I filed #166 to follow up.