Investigate better approach to value to string-ish comparison

Currently:
```c++
friend
bool
operator==(
value const& lhs,
value const& rhs) noexcept
{
return lhs.equal(rhs);
}
```

Thus, `jv == "some string"` is equivalent to `jv == value("some string")`, which allocates.
Consider adding an overload similar to one for `string` .