* added docs for vault and made trigger shorter: !vault
* added single var valuting
* Update playbooks_vault.rst
Edit pass for spelling and grammar. Ship it!
* Update playbooks_vault.rst
Typo fixes.
This change corrects problems reported by the `yamllint` linter.
Since key duplication problems were removed in 4d48711, this commit
mainly fixes trailing spaces and extra empty lines at beginning/end of
files.