Put version handling into the helpers package so it can be used by many,
and split version and suffix to make it possible to calculate the next Hugo version.
Added Version, CommitHash and BuildDate to hugolib/hugo.go and used it in build
Removed commitHash and buildDate from commands/version.go and used hugolib vars
Removed getDateFormat function from commands/version.go
Conflicts:
README.md
docs/content/templates/variables.md