Use rand-core 0.1.0-pre.0 release

Merge pull request rust-random#327 from pitdicker/rand_core_rename

Rename rand-core to rand_core

Remove 0.3 from list of versions in README

Final 0.3 release: update version number

Final 0.3 release (pre): add note to README, and update version number

Merge pull request rust-random#222 from dhardy/0.3

0.3.20 release

Merge pull request rust-random#213 from MaloJaffre/patch-2

Bump to 0.3.19

Bump version to 0.4.1; update CHANGELOG and README

Update version number in changelog [ci skip]

Version 0.3.18