* cmd/uplink: add share command to restrict an api key
This commit is an early bit of work to just implement restricting
macaroon api keys from the command line. It does not convert
api keys to be macaroons in general.
It also does not apply the path restriction caveats appropriately
yet because it does not encrypt them.
* cmd/uplink: fix path encryption for shares
It should now properly encrypt the path prefixes when adding
caveats to a macaroon.
* fix up linting problems
* print summary of caveat and require iso8601
* make clone part more clear
