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-extension.hpp b/src/security/certificate-extension.hpp
index a1aa5b6..83653ee 100644
--- a/src/security/certificate-extension.hpp
+++ b/src/security/certificate-extension.hpp
@@ -13,7 +13,9 @@
 #include "../encoding/buffer.hpp"
 #include "../encoding/oid.hpp"
 
-namespace CryptoPP { class BufferedTransformation; }
+namespace CryptoPP {
+class BufferedTransformation;
+}
 
 namespace ndn {