Reject integer lengths in json_document::parse

parse(ptr, len) compiled: len converted to allow_exceptions, and ptr was
read as a C string, past the end of a buffer without a terminating NUL.
Delete the overloads of parse, parse_copy, accept, and read that take an
integer other than bool where the flags are expected.

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

include/nlohmann/detail/view/input.hpp

@@ -59,6 +59,13 @@ struct classify_input
     // NOLINTEND(readability-avoid-nested-conditional-operator)
 };
 
+/// an integer type other than bool: a length passed where a flag is expected
+template<typename T>
+struct is_integer_not_bool : std::is_integral<T> {};
+
+template<>
+struct is_integer_not_bool<bool> : std::false_type {};
+
 /// std::basic_string guarantees a NUL at data()[size()] (the parser's sentinel)
 template<typename T>
 struct is_std_string : std::false_type {};