Add Travis CI config
Add Travis CI config

Uses a PPA with back-ported libwebp to work around https://bugs.launchpad.net/ubuntu/+source/libwebp/+bug/1108731

cmtt/sharp,leiyangyou/sharp,lovell/sharp,dtest/sharp,kevinsawicki/sharp,philip8728/sharp,mcanthony/sharp,digital-flowers/sharp-win32,digital-flowers/sharp-win32,kevinsawicki/sharp,mdimitrov/sharp,mhirsch/sharp,mdimitrov/sharp,leiyangyou/sharp,lovell/sharp,digital-flowers/sharp-win32,brandonaaron/sharp,leiyangyou/sharp,mcanthony/sharp,mdimitrov/sharp,dtest/sharp,papandreou/sharp,mdimitrov/sharp,cmtt/sharp,lovell/sharp,dtest/sharp,chrisriley/sharp,chrisriley/sharp,mdimitrov/sharp,kevinsawicki/sharp,pporada-gl/sharp,philip8728/sharp,chrisriley/sharp,cmtt/sharp,brandonaaron/sharp,mhirsch/sharp,leiyangyou/sharp,brandonaaron/sharp,chrisriley/sharp,papandreou/sharp,pporada-gl/sharp,philip8728/sharp,digital-flowers/sharp-win32,brandonaaron/sharp,papandreou/sharp,digital-flowers/sharp-win32,mhirsch/sharp,kevinsawicki/sharp,brandonaaron/sharp,mhirsch/sharp,mcanthony/sharp,dtest/sharp,papandreou/sharp,pporada-gl/sharp,digital-flowers/sharp-win32,pporada-gl/sharp,mcanthony/sharp,pporada-gl/sharp,lovell/sharp,mcanthony/sharp,chrisriley/sharp,lovell/sharp,digital-flowers/sharp-win32,kevinsawicki/sharp,philip8728/sharp,dtest/sharp,papandreou/sharp,cmtt/sharp,philip8728/sharp,lovell/sharp,leiyangyou/sharp