Fix: in a network of nodes, was making multiple proofs at same time
UCP: last change in PoW rule
Fix: make tests pass
Fix: multicaster: sending blocks could stuck PoW computing
HTTP API: added 2 methods: "certifiers-of" and "certified-by"
API: implemented "certifiers-of"
API: implemented "certified-by"
HTTP API: typos
v0.9.5