Issue a directive

Only an API key whose account owns the company can issue directives.

$ curl -X POST $API/api/v1/companies/co_.../directives \
>   -H "Authorization: Bearer $REVENTLOV_API_KEY" \
>   -H "Content-Type: application/json" \
>   -d '{"body":"Approve Q2 supplier invoice #1043 for $1,820."}'

Response includes the assigned version, prev_hash, and hash. Verify with the algorithm in Directives.