Merge pull request mbj#809 from mbj/bump/version

Change version to 0.8.23

Merge pull request mbj#797 from mbj/remove/version-requirement

Remove hard ruby version requirement

Merge pull request mbj#796 from mbj/bump/version

Change version to 0.8.21

Merge pull request mbj#778 from mbj/bump/version

Bump mutant version to 0.8.20

Merge pull request mbj#756 from mbj/fix/memoizable-test

Fix Memoizable test

Merge pull request mbj#750 from mbj/bump/version

Change mutant version to 0.8.18

Merge pull request mbj#748 from mbj/bump/version

Bump version to v0.8.17

Bump to v0.8.16

Merge pull request mbj#734 from mbj/release/v0.8.15

Bump version to 0.8.15

Merge pull request mbj#720 from mbj/fix/bump-version

Bump version to 0.8.14