Elixir Concurrency Model

Simple example of the Elixir Concurrency Model and how to handle blocking processes.

Paste the below code into a file called `concurrency_demo.ex` and run
`$ elixir concurrency_demo.ex` to run the example locally

```elixir
defmodule Log do
defp log(arg), do: IO.puts arg
def first, do: log "first"
def second, do: log "second"
def slowfirst do
:timer.sleep(1000)
first()
end
end

IO.puts "RUN 1"
Log.slowfirst()
Log.second()

# Outputs:
# $ RUN 1
# $ first
# $ second

# In "RUN 1" we see that `slowfirst` blocks `second` from running

IO.puts "RUN 2"
task = Task.async(fn -> Log.slowfirst() end)
Log.second()

# Outputs:
# $ RUN 2
# $ second
# $ first

# But in "RUN 2" we start `slowfirst` and then carry on with the script

Task.await(task) # If you don't assign task and `await`, the program will finish and you won't see the log
```