JsonString
Description
JsonString is an object that refers to a constant string in RAM.
You can see it a a supercharged const char* that supports:
- comparison operations
 - non-zero-terminated strings
 - NUL characters inside the string
 
It is similar to std::string_view.
Interface
class JsonString {
 public:
  JsonString(const char* p=0);
  JsonString(const char* p, size_t n);
  
  size_t size() const;
  const char* c_str() const;
};