remove templating & simplify error message

+ clang-format in Error files
+ Remove AnyError

samples/xmpdump.cpp

@@ -30,7 +30,7 @@ int main(int argc, char* const argv[])
         std::cout << xmpPacket << "\n";
 
         return 0;
-    } catch (Exiv2::AnyError& e) {
+    } catch (Exiv2::Error& e) {
         std::cout << "Caught Exiv2 exception '" << e << "'\n";
         return -1;
     }