New option --release to run a complete build cycle.

* build.sh: Add options --release and --log-file.  Rmeove unused
option --nightly.

For example

cd ~/s/gpg4win-test
./autogen.sh
./build.sh --release --no-sign --download --verbose

should download all files, create a traball and build form that
tarballs. The final results will then show up at

~/b/gpg4win-test-mill/binary/artifacts

The above option skip the authneticode sign step and give verbose
output. For security reasons pulling from a git repo is not yet
implemented.