Add --head-only and --package-name options.

Adds a new --head-only option which can be used to make Delorean
build only the most recent Git commit for each project.

Also adds a new --package-name option which can be used to
build only a specific package.

As part of these changes the getinfo function was refactored to
return a project "to process" list rather than passing one into
the function. We also moved some of the logic out of getinfo to
make things cleaner.