Updated pypy to 2.3.1 and added pypy3
Updated pypy to 2.3.1 and added pypy3

Both are marked (unsupported, experimental).
jamarparris/heroku-buildpack-python-swig,monological/heroku-buildpack-python-opencv,samuelhavron/heroku-buildpack-python,brightforme/heroku-buildpack-python,vlidholt/heroku-buildpack-scipy,benmurden/heroku-buildpack-python-ember,cloudfoundry/python-buildpack,cloudfoundry/python-buildpack,TipWander/heroku-buildpack-geodjango,samuelhavron/heroku-buildpack-python,kowito/python-buildpack,mobify/heroku-buildpack-python-swig,samuelhavron/heroku-buildpack-python,ad-m/heroku-buildpack-python,joshisa/python-buildpack,hsr-ba-fs15-dat/heroku-buildpack,samuelhavron/heroku-buildpack-python,rollokb/heroku-buildpack-python,RobertSundling/heroku-buildpack-python-nginx,Nazanin84/python-buildpack,nikita-pivovarov/heroku-buildpack-python-ldap,icoxfog417/heroku-buildpack-python,markine/heroku-buildpack-python,nwkotto/geodjango-buildpack-with-geos,agriffis/heroku-buildpack-python,HousekeepLtd/heroku-buildpack-python,18F/python-buildpack,edmorley/heroku-buildpack-python,nadirizr/heroku-buildpack-python-gulp,jimlindeman/python-buildpack-collectd,predata/heroku-buildpack-scipy,Nazanin84/python-buildpack,Apogaea/heroku-buildpack-python,kvarga/heroku-buildpack-python,cclauss/heroku-buildpack-python,edenspiekermann-amsterdam/heroku-buildpack-python,liyanchang/cloudfoundary-buildbot-buildpack,junyoed/heroku-buildpack-python,benmurden/heroku-buildpack-python-ember,wbrefvem/heroku-buildpack-python,blazekadam/open2,joshisa/python-buildpack,pkumar-appd/python-buildpack,liyanchang/cloudfoundary-buildbot-buildpack,jvenezia/heroku-buildpack-python,Scalingo/python-buildpack,Stibbons/heroku-buildpack-python-installer,slorg1/heroku-buildpack-python,zakdoek/heroku-buildpack-django,papaeye/heroku-buildpack-python-bower,maxcountryman/heroku-buildpack-python,18F/python-buildpack,manufacturedba/heroku-buildpack-python,gitricko/apt-python-buildpack,ruscoder/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,Nazanin84/python-buildpack,skilljar/heroku-buildpack-python,resmio/heroku-buildpack-geodjango,nicktimko/heroku-buildpack-scipy,joshowen/heroku-buildpack-python,benjaminfox/heroku-buildpack-python-geoip,andela-brotich/wger-buildpack-python,ephemerallabs/heroku-buildpack-python,kowito/python-buildpack,ojacobson/heroku-buildpack-python,Scalingo/python-buildpack,oberlin/heroku-buildpack-python,andrespires/python-buildpack,dubsmash/heroku-buildpack-python,doda/heroku-buildpack-python,thenovices/heroku-buildpack-scipy,andrespires/python-buildpack,samuelhavron/heroku-buildpack-python,samuelhavron/heroku-buildpack-python,marianzange/heroku-buildpack-python,beni55/heroku-buildpack-python,wbrefvem/heroku-buildpack-python,soapril/heroku-buildpack-python,joshisa/python-buildpack,swanson/heroku-buildpack-python-ortools,miraculixx/heroku-buildpack-python,marcospy/heroku-buildpack-scipy,joshfriend/heroku-buildpack-python,alexflanagan/operand-buildpack-python,samuelhavron/heroku-buildpack-python,liyanchang/cloudfoundary-buildbot-buildpack,ianyh/heroku-buildpack-python-bower,gitricko/apt-python-buildpack,buildbot/buildbot-master-buildpack,pmclanahan/heroku-buildpack-python-peep,18F/python-buildpack,ekkleesia2/heroku-buildpack-python,heroku/heroku-buildpack-python,tommyvn/heroku-buildpack-python,adamroth/heroku-buildpack-python-pdftk,ad-m/heroku-buildpack-python,doda/heroku-buildpack-python,ywarezk/heroku-buildpack-geodjango,lukaszkorecki/heroku-buildpack-python,loanzen/heroku-buildpack-python,zakdoek/heroku-buildpack-django,Tiger66639/buildbot-master-buildpack,bobsilverberg/heroku-buildpack-python-peep,mythmon/heroku-buildpack-python-nodejs,alexflanagan/operand-buildpack-python,nemesiscodex/heroku-buildpack-python,stalnacke/heroku-buildpack-python,AltSchool/heroku-buildpack-python,marcospy/hackathon-globo-app,martingascon/heroku-buildpack-python,cortexintel/heroku-buildpack-scipy,scrapinghub/scrapinghub-buildpack-scrapy,YoApp/heroku-buildpack-python-twemproxy,jimlindeman/python-buildpack-collectd,dvreed/heroku-buildpack-python-ldap,PerceptumNL/heroku-buildpack-python,cloudfoundry/python-buildpack,river-jade/heroku-buildpack-scipy,AltSchool/heroku-buildpack-python,andrespires/python-buildpack,dulaccc/heroku-buildpack-geodjango,swils/heroku-buildpack-python,amanjain/heroku-buildpack-python-with-django-bower,samuelhavron/heroku-buildpack-python,gaumire/heroku-buildpack-python,pkumar-appd/python-buildpack,arnaudlimbourg/heroku-buildpack-python,marcospy/hackathon-globo-app,projetoeureka/heroku-buildpack-scipy,igroff/heroku-buildpack-python,cdht/heroku-buildpack-python,rapilabs/heroku-buildpack-python,grivescorbett/heroku-buildpack-python,xica/heroku-buildpack-scipy,brianthomas/heroku-buildpack-textmining,ryanhiebert/heroku-buildpack-python,maciejgryka/heroku-buildpack-spcedge,WonderThink/heroku-buildpack-python-ffmpeg-geoip,gitricko/apt-python-buildpack,driftyco/heroku-buildpack-sphinx,pebble/cloudpebble-buildpack,integricho/heroku-buildpack-python-ffmpeg2.1-with-codecs,marcospy/hackathon-globo-app,heroku/heroku-buildpack-python,rbtying/heroku-buildpack-python,liyanchang/buildbot-master-buildpack,kowito/python-buildpack,DylanLukes/heroku-buildpack-python,HanSooloo/heroku-buildpack-python,plangrid/heroku-buildpack-python,smalleats/heroku-buildpack-python,Brogency/heroku-buildpack-python-gulp,pkumar-appd/python-buildpack,jimlindeman/python-buildpack-collectd,pwdel1/heroku-buildpack-scipy,Mause/heroku-buildpack-python