add failing test for before_release

See [rt.cpan.org #84744].
make before_release trigger during release

Fixes [rt.cpan.org #84744].
add failing test for PreviousVersionProvider error

See [rt.cpan.org #84359].
throw correct error for no PreviousVersionProvider

Fixes [rt.cpan.org #84359].
more PreviousVersionProvider documentation

Make it more obvious that the user must reference a
PreviousVersionProvider-consuming plugin in dist.ini.

Partially addresses [rt.cpan.org #84359].
Merge commit '93be1044ea2e4da7a86'
Merge remote-tracking branch 'remotes/github/pr/1'
release preps
v0.1.1

    [BUGS FIXES]
    - Forgot BeforeRelease role (oops). [RT#84744, patch by Alex Peters]
    - Clean up error messages and improve docs for PreviousVersionProvider. [GH#1, patch by Alex Peters]