replace ntfromstruct() with NamedTuple method

[Lincoln-Hannah]

using WhereTraits

@traits NamedTuple( x ) where isstructtype(typeof(x)) = ntfromstruct( x )

The functionality in WhereTraits.jl would allow ntfromstruct() to be replaced with a NamedTuple() method.
This reduces the number of interface functions, and seems nice to me.
But I'm not an expert.

[JeffreySarnoff]

I am avoiding overloading NamedTuple directly. It is a type exported from Base, so altering its behavior (or adding a constructor) is considered type piracy. I appreciate your focus on this, thanks.