Show build status of master branch in README
Show build status of master branch in README

This fixes #316 with the solution @marcjansen suggested.
geographika/geoext2,m-click/geoext2,marcjansen/geoext2,bentrm/geoext2,marcjansen/geoext2,chrismayer/geoext2,geoext/geoext2,chrismayer/geoext2,geographika/geoext2,geoext/geoext2,annarieger/geoext2,bentrm/geoext2,m-click/geoext2,annarieger/geoext2