Add support for "profiles" in user-specific directories.

[SimonSapin]

See doc-comment.

Bumping to 2.1 as it’s a new feature. (By the way, what does "pre" mean to you in version numbers?)

[whitequark]

You don't have to bump, because the currently published version is a pre-release. See paragraph 9 on http://semver.org/.

[whitequark]

Otherwise LGTM.

[SimonSapin]

Amended. (Should Cargo handle pre-releases specially?)

[whitequark]

I worked under assumption that it does (i.e. * or ~> 2.0 do not include pre-releases; this is what e.g. Ruby's Bundler does). Is that not the case?

[SimonSapin]

I don’t know. @alexcrichton, how does Cargo treat pre-release version numbers?

[alexcrichton]

Currently Cargo doesn't treat pre-release versions specially, the behavior just falls out of the standard logic for comparing semver versions

[whitequark]

@alexcrichton Actually, it does not. If I put xdg = "2.0" or xdg = ">= 2.0" in Cargo.toml, Cargo selects 2.0.0-pre5, which is in clear contradiction of the semver spec, paragraph 11