Add curryN to the helper functions

[evilsoft]

Limit Dem

This PR address issue#10.

It adds a curryN function to limit the number of arguments to a function or deal with N-ary functions or defaulted arguments.

// limit to default
const times10 = curryN(1,
  (x, y=10) => x * y
)
times10(23) // 230

// arg spread
const scaleSum = curryN(4,
  (s, ...args) => args.reduce((x, y) => x + y, 0) * s
)
const doubleSum = scaleSum(2)

scaleSum(10, 3)(4, 5) // 120
doubleSum(3, 4)(5) // 24

// N-ary
const maxOf3 = curryN(3, Math.max)
maxOf3(3)(20)(0) // 20

This function will not keep currying until a non-function is returned like curry does.

const f =  curryN(3,
  (x, y) => z => [ x, y, z ]

// the last argument is applied to the outer function and
// therefore thrown away, resulting in the inner function
// being returned.
f(3, 4, 5) // z => ...

[flintinatux]

I like the look of this. Since it's OSS, you oughta hook up some free Travis for your specs to check PR's.

[evilsoft]

@flintinatux 🍬 idea!

[evilsoft]