script: generate/archive versioned copy of public/

Support creating and deploying archive copies of earlier versions of the Lab framework.

Create an archive of the public dir in: ./archived/<short-SHA>/public

  $ script/create-archived-public-dir.sh

Create an archive of the public dir in: ./archived/v0.5.1/public

  $ script/create-archived-public-dir.sh v0.5.1

Create symbolic links in the public dir for each archived copy of public:

  $ create-symbolic-links-to-archives.rb