Fix two warnings on raised by Visual Studio 2015 compiler + disable -Wall and -Wextra when using Visual Studio compiler

CMakeLists.txt

@@ -31,9 +31,12 @@ target_include_directories(json-schema-validator
 target_compile_features(json-schema-validator
     PUBLIC
         cxx_range_for) # for C++11 - flags
+# Enable more compiler warnings, except when using Visual Studio compiler
+if(NOT MSVC)
     target_compile_options(json-schema-validator
     PUBLIC
-        -Wall) # bad, better use something else based on compiler type
+        -Wall -Wextra)
+endif()
 target_link_libraries(json-schema-validator
     PUBLIC
         json-hpp)

app/json-schema-validate.cpp

@@ -93,7 +93,7 @@ int main(int argc, char *argv[])
 	json document;
 
 	try {
-		document << std::cin;
+        std::cin >> document;
 		validator.validate(document);
 	} catch (std::exception &e) {
 		std::cerr << "schema validation failed\n";

src/json-validator.cpp

@@ -344,7 +344,7 @@ void json_validator::validate(const json &instance, const json &schema_, const s
 		try {
 			validate(instance, attr.value(), name);
 			ok = false;
-		} catch (std::exception &e) {
+        } catch (std::exception &) {
 			ok = true;
 		}
 		if (!ok)