some question about charReader

When I write testcases in #1095, I find some problems:

1. comment

I find the comments can be inserted anywhere except the place after the key value of an object. for example:
the input is:

char const doc[] = "//comment1\n [ //comment2\n \"value\" //comment3\n,"
                       " //comment4\n true //comment5\n ] //comment6\n";
char const doc[] = "//comment1\n { //comment2\n \"property\" :"
                   " \"value\" //comment3\n } //comment4\n";

after parse the doc, then print root[0], we get:

  //comment2
  "value" //comment3

Is this an ideal result? we should update the Wiki and tell the user what should be concerned when they add the comments.

2. Value::LargestUInt(Value::maxLargestInt) (9223372036854775807 )

https://github.com/open-source-parsers/jsoncpp/blob/d2e6a971f4544c55b8e3b25cf96db266971b778f/src/lib_json/json_reader.cpp#L1605

  if (isNegative) {
    // We use the same magnitude assumption here, just in case.
    const Value::UInt last_digit = static_cast<Value::UInt>(value % 10);
    decoded = -Value::LargestInt(value / 10) * 10 - last_digit;
  } else if (value <= Value::LargestUInt(Value::maxLargestInt)) {
    decoded = Value::LargestInt(value);
  } else {
    decoded = value;
  }
  return true;
}

In order to cover this line, we add the testcase:

{
   char const doc[] = "[9223372036854775808]";
   bool ok = reader->parse(doc, doc + std::strlen(doc), &root, &errs);
   JSONTEST_ASSERT(ok);
   JSONTEST_ASSERT(errs.empty());
   JSONTEST_ASSERT_EQUAL(9223372036854775808, root[0]);
}

and get the error message:

FAILED: jsoncpp_test@exe/src_test_lib_json_main.cpp.o
c++ -Ijsoncpp_test@exe -I. -I.. -I../include -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -std=c++11 -g -MD -MQ 'jsoncpp_test@exe/src_test_lib_json_main.cpp.o' -MF 'jsoncpp_test@exe/src_test_lib_json_main.cpp.o.d' -o 'jsoncpp_test@exe/src_test_lib_json_main.cpp.o' -c ../src/test_lib_json/main.cpp
../src/test_lib_json/main.cpp:2861:55: warning: integer constant is so large that it is unsigned
     JSONTEST_ASSERT_EQUAL(9223372036854775808, root[0]);
                                                       ^
In file included from ../src/test_lib_json/main.cpp:14:0:
../src/test_lib_json/jsontest.h: In instantiation of ‘JsonTest::TestResult& JsonTest::checkEqual(JsonTest::TestResult&, T, U, const char*, unsigned int, const char*) [with T = __int128; U = Json::Value]’:
../src/test_lib_json/main.cpp:2861:5:   required from here
../src/test_lib_json/jsontest.h:178:7: error: call of overloaded ‘Value(__int128&)’ is ambiguous

Is this a bug? How can we remove this error?

3 some redundant code

  while (current != end) {
    Char c = *current++;
    if (c == '"') {
      break;
    } else if (c == '\\') {
      if (current == end)
        return addError("Empty escape sequence in string", token, current);
      Char escape = *current++;
      switch (escape) {

I think we can never get this line:
https://github.com/open-source-parsers/jsoncpp/blob/d2e6a971f4544c55b8e3b25cf96db266971b778f/src/lib_json/json_reader.cpp#L1657
and this line:
https://github.com/open-source-parsers/jsoncpp/blob/d2e6a971f4544c55b8e3b25cf96db266971b778f/src/lib_json/json_reader.cpp#L1660

Start with the comment and number parsing paths in src/lib_json/json_reader.cpp, then inspect the related cases in src/test_lib_json/main.cpp and the assertion helper in src/test_lib_json/jsontest.h. Reproduce the comment behavior and large-integer test result, and verify the two string-parser branches identified by their source links. Done means the questions are resolved with focused tests or documentation updates where appropriate.