1.5.1 prep.
Merge pull request #328 from mhaskel/1.5.1-prep

1.5.1 prep.
Prepare a 1.5.2 release.
Merge pull request #331 from apenney/152-release

Prepare a 1.5.2 release.
Fix readme typo.
Merge pull request #332 from zacharyalexstern/fix_readme_typo

Fix readme typo.
Merge remote-tracking branch 'upstream/1.5.x'
Prep for 1.6.0 release.