Rename 'debops-install' to 'debops-update'
Rewrite 'debops-update' script with new features

Script now actually can update installed playbooks and roles, can find
them in several different locations (local directory,
$HOME/.local/share/debops, directory specified at the command line) and
install them if necessary.
Merge pull request #17 from drybjed/install_to_update

Rewrite 'debops-install' and rename it to 'debops-update'
More repeating code into separate functions
Make pushd/popd commands less noisy by default
Merge pull request #18 from drybjed/backup_fix

Small fixes in the backup script
Update the debops-update description
Reword the debops-update help
Merge pull request #19 from nickjj/docs

Update the debops-update description
Restructure the opening sentence to avoid the widow
Remove another widow from debops-update's description
Merge pull request #20 from nickjj/docs

Restructure the opening sentence to avoid the widow