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oval: add textfilecontent54 objects

Claircore has need to interrogate the corresponding textfilecontent54
tests, so implement the referenced objects to make the lookup heuristics
easier.

Signed-off-by: Hank Donnay <[email protected]>

oval: add verifyfiles_object types

Signed-off-by: Hank Donnay <[email protected]>

oval: add Test interface and implementation

Signed-off-by: Hank Donnay <[email protected]>

oval: add additional date format as seen in the wild

This adds support for a particularly annoying format that doesn't even
specify a single date.

Signed-off-by: Hank Donnay <[email protected]>

Add dpkg support (#7)

This PR adds several data structures and memo methods
to support parsing dpkginfo oval structures.

Signed-off-by: louis <[email protected]>

Co-authored-by: louis <[email protected]>

bump version with empty-date fix

This version adds a custom date type for transparent unmarshaling.

oval: add additional test types

Red Hat recently started using additional test types in their oval
database. These changes allow the new database to be walked again.