making converge multiarg for greater composition capabilities, as R.compose, R.pipe etc.

As discussed in #527, converge as a multi arg function would enhance composition capabilities, while staying backwards compatible.
```js
// R.I2 = R.argN(1)
// R.I3 = R.argN(2)
redSquare = R.converge(Rectangle, R.I, R.I2, R.I3, R.I3, R.always(0xFF0000));
redSquare(0,0, 100);  // paints red square at 
                      //    x=0
                      //    y=0
                      //    width = 100
                      //    height set to equal width=100 by converge (width and height receive R.I3 !)
```

I'm not sure the new signature is correct.
All old converge tests **pass**, however i would need to add tests that also make use of the new variadic capabilities of R.converge. If you guys are cool with this extension in general, i will write some tests that cover multi args.