My branch `pin` of repo `https://git.spwhitton.name/propellor` adds

- `Apt.suiteAvailablePinned`
- `Apt.pinnedTo`
- `File.containsBlock`
- a haddock for `File.containsLines`

There is one TODO in a comment that relates to propellor's algebraic data types.  I'd be grateful for help with that.  --spwhitton

> merged, thanks. [[done]] --[[Joey]]
