Added simple mix task to compile solidity test files

README.md

@@ -26,5 +26,5 @@ solc --version
 
 Then if you've made changes to the example contracts you can compile them like this:
 ```
-solc -o test/examples/build --abi --bin test/examples/contracts/* --overwrite
+mix solc
 ```

mix.exs

@@ -56,3 +56,13 @@ defmodule ExW3.MixProject do
     ]
   end
 end
+
+defmodule Mix.Tasks.Solc do
+  use Mix.Task
+
+  @shortdoc "Runs the solc compiler to create binary and abi of all contracts. Outputs to build directory"
+  def run(_) do
+    # calling our Hello.say() function from earlier
+    Mix.Shell.IO.cmd("solc -o test/examples/build --abi --bin test/examples/contracts/* --overwrite")
+  end
+end