Option to move filter to format in merge

[mbhall88]

The filter logic in merge is really nice

-F, --filter-logic x|+            Remove filters if some input is PASS ("x"), or apply all filters ("+") [+]

but I want to suggest another option which would move the filters to a new FORMAT field. My use case for example is I have merged the VCF for four samples and would like to be able to check which samples had a filter at a position. At the moment, using "+" I just know that at least one sample had a filter, but not which sample.

If there is an alternate way of doing this I would love to know.