encoding: Extending Block and EncodingBuffer interfaces

Now it is possible to use constructors to create Block from
EncodingBuffer and EncodingBuffer from Block.

Block->EncodingBuffer conversion is potentially dangerous and should be
used only in exceptional cases, such as Data packet encoding: to encode
the signed part first and then extend signed part with signature and
other related fields.

Change-Id: I5a13bf0c196ecd0d45dfa14c4cb6f4a9f612420c
diff --git a/src/common.hpp b/src/common.hpp
index 647e306..8d26a14 100644
--- a/src/common.hpp
+++ b/src/common.hpp
@@ -54,6 +54,10 @@
 using std::make_shared;
 using std::enable_shared_from_this;
 
+using std::static_pointer_cast;
+using std::dynamic_pointer_cast;
+using std::const_pointer_cast;
+
 using std::function;
 using std::bind;
 using std::placeholders; // _1, _2, ..
@@ -79,6 +83,10 @@
 using boost::make_shared;
 using boost::enable_shared_from_this;
 
+using boost::static_pointer_cast;
+using boost::dynamic_pointer_cast;
+using boost::const_pointer_cast;
+
 using boost::function;
 using boost::bind;