Validate value of GPG :key_id

The value of `:key_id` must be an hexadecimal string of length 8, 16,
or 40.
Update GPG tests to use valid key IDs
Test for invalid GPG key IDs
Add Maintenance Latest
Adobe Digital Editions 4.0
document `uninstall :trash`
incidental Markdown formatting
document `tags` stanza
add `tags :vendor` to Cask google-chrome.rb
add `tags :name` to Cask smlnj
sync `license` doc with `tags`

re: current lack of front-end interface to the relevant Cask data
update for Couchbase Server 3.0.0 versions ʕノ◔ϖ◔ʔノ
Upgrade Alfred 2.app to v2.5_299
Add MacScale latest

- class name now == Macscale as per [Naming
Ref](https://github.com/caskroom/homebrew-cask/blob/master/doc/CASK_NAMING_REFERENCE.md)
- version now == :latest and sha256 == :no_check as per. [Contributing](https://github.com/caskroom/homebrew-cask/blob/master/CONTRIBUTING.md#cask-stanzas)
bump 1password to 4.4.2
Merge pull request #6502 from jm3/macscale

Add MacScale 1.6.4
Merge pull request #6511 from deepsweet/alfred

Upgrade Alfred 2.app to v2.5_299
Merge pull request #6512 from fly/1p

bump 1password to 4.4.2
Merge pull request #6508 from brianshumate/master

Update for Couchbase Server 3.0.0 versions
Merge pull request #6505 from glimpsed/patch-1

Adobe Digital Editions 4.0