Add Yandex Metrica Provider (http://metrika.yandex.com/).
Update Contributing.md
Update Makefile
added yandex metrica
release: 0.17.7

    propagating traverse isodate fix
adding a date test
customerio: added preliminary group support
mixpanel has deprecated the track_pageview method, removing it!
Merge pull request #298 from segmentio/mixpanel-pageview

mixpanel deprecated the track_pageview method, removing it!
Fixing two issues with google analytics universal: ip anonymization and empty cookie domain string
Merge pull request #300 from segmentio/ga-universal-fixes

Fixing two issues with google analytics universal
0.17.9
adding event emitter to analytics prototype and emitting on all actons via _invoke
adding emit ready and initialize, and adding tests for alias, pageview, ready, and initialize
bump version to 0.18.0
Merge pull request #301 from segmentio/eventemitter

adding event emitter to analytics prototype
0.18.0 build