Fix clang-tidy and clang 3.4/3.5 failures in the custom number type changes

Parenthesize n % 10 in integer_to_string for
readability-math-missing-parentheses, and give class_int non-template
constructors (as absl::int128 has): clang 3.4 and 3.5 reject the defaulted
basic_json::data() constructor for a number type with template constructors.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/output/binary_writer.hpp

@@ -920,7 +920,7 @@ class binary_writer
         std::string result;
         do
         {
-            result.push_back(static_cast<char>('0' + n % 10));
+            result.push_back(static_cast<char>('0' + (n % 10)));
             n = static_cast<NumberType>(n / 10);
         }
         while (n != 0);

single_include/nlohmann/json.hpp

@@ -22655,7 +22655,7 @@ class binary_writer
         std::string result;
         do
         {
-            result.push_back(static_cast<char>('0' + n % 10));
+            result.push_back(static_cast<char>('0' + (n % 10)));
             n = static_cast<NumberType>(n / 10);
         }
         while (n != 0);

tests/src/unit-custom-number-types.cpp

@@ -34,12 +34,17 @@ class class_int
     // trivial, like the 128-bit integer classes: the value is stored in a union
     class_int() = default;
 
-    // implicit from built-in integers and explicit from floats, like absl::int128
+    // implicit from built-in integers and explicit from floats, like absl::int128;
-    template<typename T, typename std::enable_if<std::is_integral<T>::value, int>::type = 0>
+    // non-template overloads (as absl::int128 has) because clang 3.4 and 3.5
-    class_int(T v) : value(static_cast<std::int64_t>(v)) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    // reject basic_json's defaulted data() for a number type with template
-
+    // constructors
-    template<typename T, typename std::enable_if<std::is_floating_point<T>::value, int>::type = 0>
+    class_int(int v) : value(v) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
-    explicit class_int(T v) : value(static_cast<std::int64_t>(v)) {}
+    class_int(unsigned v) : value(v) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    class_int(long v) : value(v) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    class_int(unsigned long v) : value(static_cast<std::int64_t>(v)) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    class_int(long long v) : value(v) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    class_int(unsigned long long v) : value(static_cast<std::int64_t>(v)) {} // NOLINT(google-explicit-constructor,hicpp-explicit-conversions)
+    explicit class_int(double v) : value(static_cast<std::int64_t>(v)) {}
 
     template<typename T, typename std::enable_if<std::is_arithmetic<T>::value, int>::type = 0>
     explicit operator T() const