Introduce namespace langutil in liblangutil directory.

Also:
- Use {}-style list initialisation for SourceLocation construction
- Introduce new system includes
- Changes the API of the Scanner to take source as value (with move) as opposed to as a reference

libsolidity/ast/ASTPrinter.cpp

@@ -28,6 +28,7 @@
 #include <boost/algorithm/string/join.hpp>
 
 using namespace std;
+using namespace langutil;
 
 namespace dev
 {