Add metadata output to tacl diff/intersect/report

[ajenhl]

Add an option to tacl diff/intersect/report to output the results to the specified file rather than stdout, and in addition output metadata about the operation to a file with the same name but different extension. This metadata would consist of:

• The catalogue entries used in the query (not the name of the file, but the actual texts and labels).
• The date the query was run.
• The date each text used in the query was last updated in the database.
• The hash of each text from the database.
• The date each text used in the query was last updated in the corpus.
• The hash of each used text in the corpus.
• The type of query (diff or intersect).
• The tokenizer used.
• The report operations applied.

In the case of tacl report, the metadata output would include any metadata available for the query being operated on.

[ajenhl]

An advantage to doing this is that it allows for warnings to be generated when the user does something inadvisable. For example, if some results are being reduced, and one or more sources of those results have already been reduced.