exceptions: Make Tlv::Error a base class for all packet-processing exceptions

This commit also includes a number of code style fixes.

Change-Id: I44f83915e733b43d5f43b4266902c8262e928d91
Refs: #1528
diff --git a/src/security/certificate.hpp b/src/security/certificate.hpp
index dc96879..157b878 100644
--- a/src/security/certificate.hpp
+++ b/src/security/certificate.hpp
@@ -17,7 +17,8 @@
 
 namespace ndn {
 
-class Certificate : public Data {
+class Certificate : public Data
+{
 public:
   class Error : public std::runtime_error
   {