[elixir] Add word cound elixir exercise
[ellixir] Add first pass of word_count, one failing test

I wanted to commit my tinkering with the Elixir pipe operator so I could
then concentrate on fixing my regex
[elixir] Tweak the word_count regular expression

Submission: http://exercism.io/submissions/8131ccb23aa739cf6953d533
[elixir] Extract functions for word_count transform

I think the actual count/1 function body reads pretty well. I am a bit
annoyed by the cound_words/1 function, wishing it could simply be
count/1 with a guard clause checking for a list:

```elixir
defp count(words) when is_list(words) do
  # ...
end
```

But you seemingly can't have both a public and private function with the
same signature, ¯\_(ツ)_/¯
[elixir] Simplify count_words function

Use the Dict.update/4 function instead of checking for the extistence of
a key.

Also, use the fuction capture operator to partially apply `Kernel.left +
right` as the Dict.update function argument. This removes the need of
explicitly writing out an anonymous function.

See http://elixir-lang.org/getting_started/6.html#toc_5

Submission: http://exercism.io/submissions/697f500b3f752466960b155e