Add relationships for ALPM packages (arch linux)

[wagoodman]

Partially implements #572

This PR primarily adds dependency relationships for ALPM (arch linux) packages, associating only installed packages. The ALPM package metadata will describe all 'provides' and 'depends' elements that are used for relationship creation. This is consistent with other OS package catalogers doing the same thing, and allows for cases where partial dependencies are installed (thus there is not a complete relationship graph) at least the underlying package information that persists the desired dependency state would be captured.

This PR additionaly makes the following fixes:

• The Backups field on ALPM metadata was not being populated (the wrong reader was referenced). This has been fixed
• To account for additional source, refactoring the main parser path was necessary to keep linters happy
• A small ruleguard linter correction was made (instead of checking for Closer twice, we check for Closer and Reader)
• All instances of []AlpmFileRecord behave the same way now: empty collections are allocated (instead of remaining nil). Ideally these fields would be omitempty, however, that would be a breaking change and is not allowed at this time.