Add elixir implementation

[Munksgaard]

It is very slow... Here's the result of running make on my laptop:

Name             ips        average  deviation         median         99th %
irreg          0.110         9.08 s     ±2.55%         9.08 s         9.24 s
rgbbox        0.0591        16.91 s     ±0.00%        16.91 s        16.91 s

[athas]

Elixir isn't really a parallel functional language, but I suppose it's close enough.

I trust this code is reasonable enough that the Elixir people won't come running and be mad at me, right?

I'll merge it if I manage to run it on my own machine.

[Munksgaard]

I trust this code is reasonable enough that the Elixir people won't come running and be mad at me, right?

I probably wouldn't publish the numbers loud and proud yet. It doesn't seem like it should be this slow. I'll take another look at some point next week and see if I can speed it up, but I just wanted to commit my work somewhere for now.

I'll merge it if I manage to run it on my own machine.

I think nix-shell -p elixir erlang --run make should be enough.

[athas]

I get this:

Name             ips        average  deviation         median         99th %
irreg          0.148         6.76 s     ±0.85%         6.76 s         6.80 s
rgbbox         0.112         8.89 s     ±0.07%         8.89 s         8.89 s