src: Updating code style to conform (more or less) to ndn-cxx style

Also, adding .clang-format that describes the applied style. Note that
this style requires a slightly customized version of clang-format.
diff --git a/examples/custom-apps/custom-app.hpp b/examples/custom-apps/custom-app.hpp
index 86f7bb4..5d05e99 100644
--- a/examples/custom-apps/custom-app.hpp
+++ b/examples/custom-apps/custom-app.hpp
@@ -37,32 +37,31 @@
  *
  * When an Interest is received, it is replied with a Data with 1024-byte fake payload
  */
-class CustomApp : public ndn::App
-{
+class CustomApp : public ndn::App {
 public:
   // register NS-3 type "CustomApp"
   static TypeId
-  GetTypeId ();
-  
+  GetTypeId();
+
   // (overridden from ndn::App) Processing upon start of the application
   virtual void
-  StartApplication ();
+  StartApplication();
 
   // (overridden from ndn::App) Processing when application is stopped
   virtual void
-  StopApplication ();
+  StopApplication();
 
   // (overridden from ndn::App) Callback that will be called when Interest arrives
   virtual void
-  OnInterest (Ptr<const ndn::Interest> interest);
+  OnInterest(Ptr<const ndn::Interest> interest);
 
   // (overridden from ndn::App) Callback that will be called when Data arrives
   virtual void
-  OnData (Ptr<const ndn::Data> contentObject);
+  OnData(Ptr<const ndn::Data> contentObject);
 
 private:
   void
-  SendInterest ();
+  SendInterest();
 };
 
 } // namespace ns3