A memoization macro (defmemo) for Elixir.

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Adapted from : (Gustavo Brunoro)

I found Gustavo's Gist when looking at memoization and elixir and fixed it
to work with version 1.0.x. Since then I've fixed a few of the problems with
the original implementation:

- will correctly memoize the results of functions with identical signatures 
  but in different modules.

- will work with 'when' guard clauses in function definitions. (That was fun!) 

- Added lots of lovely tests.


Add defmemo to your mix.exs file:

    {:defmemo, "~> 0.1.0"}

And run:
    mix deps.get

Before *using* a defmemo'd function start_link must be called. e.g. 


or you can add :defmemo into the applications section of your mix.exs:

    [applications: [:logger, :defmemo]]


    defmodule FibMemo do
      import DefMemo
      defmemo fibs(0), do: 0
      defmemo fibs(1), do: 1
      defmemo fibs(n), do: fibs(n - 1) + fibs(n - 2)

      def fib_10 do

As you would expect for something like fibs, memoization provides dramatic
performance improvements:

    fib (unmemoized)
    function -> {result, running time(μs)}
    fibs(30) -> {832040, 31089}
    fibs(30) -> {832040, 31833}

    FibMemo (memoized)
    fibs(30) -> {832040, 79}
    fibs(30) -> {832040, 3}
    fibs(50) -> {12586269025, 103}
    fibs(50) -> {12586269025, 3}

Note that these have also improved from version 0.1 to 0.1.1

- Add test for supervisor crashing.
- Look at injecting the type of result table used.
- Better documentation.
- More tests (alwaaaays with the testing!)
- Test with some biger data (e.g. for something like web crawling)

- ~~Supervisor ~~
- ~~Redis Based ResultTable - I've been playing with this - obviously there are
  limitations on type and it's slower than gen server but there are of course
  circumstances where it could be useful but for the most part its not a good