add Slack notification to .travis.yml
fix intermittent build failures (maybe). closes #1407
Merge pull request #1414 from boneskull/mocha-1407

fix intermittent build failures (maybe). closes #1407
add a CONTRIBUTING.md.  closes #882
Merge pull request #1415 from boneskull/issue/882

add a CONTRIBUTING.md.  closes #882
Fix buffer diffs (closes #1132, closes #1433)
add setImmediate/clearImmediate to globals; closes #1435
fix bad markdown in CONTRIBUTING.md
fix more bad markdown in CONTRIBUTING.md
fix throwing undefined/null now makes tests fail, fixes #1395