security (minor): In addCertificate, fix typo in a comment.
security (minor): In NoVerifyPolicyManager.checkSigningPolicy, fix typo in doc comment.
security (minor): In SelfVerifyPolicyManager.checkVerificationPolicy fix a typo in the doc comment.
security (minor): In SelfVerifyPolicyManager.verify, remove an old unneeded comment.
security (minor): In SelfVerifyPolicyManager.verify, the call to verifySha256WithRsaSignature already returns a boolean.
Merge branch 'master' of https://github.com/named-data/PyNDN2 into DEREncoder