util: Fix bug in MemoryContentCache for multiple add: Need to correctly use field _staleTimeMilliseconds.
util: In MemoryContentCache, fix bug for calling onDataNotFound.
Merge branch 'master' of https://github.com/named-data/PyNDN2 into DEREncoder
Added IdentityCertificate as a subclass of Certificate
Changing method on certificate to getPublicKeyInfo to match ndn-cpp