Change to Official Transformer Protocol

[kevinbeaty]

Change transducers implementation to support "Official Transformer Protocol" discussed in cognitect-labs/transducers-js#20 . Both transducers.js and transducers-js have been updated to support it (my libraries to follow soon).

Summary of changes:

// anywhere you use a transformer
// (including transducer implementations)
var xf = {
   init: function()
   step: function(acc, item)
   result: function(acc)
}
// becomes
var xf = {
   '@@transducer/init': function()
   '@@transducer/step': function(acc, item)
   '@@transducer/result': function(acc)
}
// reduced wrapper object changes from 
{
   value: acc,
   __transducers_reduced__: true
}
// to
{
   '@@transducer/value': acc,
   '@@transducer/reduced':true
}

Obviously, there is room to generalize this. This may be a good opportunity to reduce the redundancy and consider other transducer implementation strategies (other than .prototype) as @CrossEye and @megawac brought up in the initial transducers PR

[CrossEye]

I do love interoperability! 😄