Specify MIME type for sigsum proofs
It would be nice if there were a application/sigsum-proof
MIME type registered for the output/input data produced/consumed by this tool. To define that, it would be nice (but not required) to make some statement related to stability of the formats, so they don't change arbitrarily or without some versioning. Establishing a de-factor file extension may be helpful too; *.sigsum-proof
or *.ssp
?