build.sh: use sbuild instead of pbuilder
build.sh: make doclean call explicit
build.sh: improve the cleanup of package build files
build.sh: move the sbuild output from the parent directory
build.sh: create a Packages.gz file
build.sh pbuild: create a signed reprepro repository
build.sh: support opening a shell to the sbuild image
build.sh: use RELEASE-ppa for the reprepro archive
build.sh pbuild: support local packages
build.sh pbuild: build arch=all packages as well