Adding libmodbus.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/libmodbus.rb

@@ -0,0 +1,25 @@
+require 'formula'
+
+# Documentation: https://github.com/mxcl/homebrew/wiki/Formula-Cookbook
+# PLEASE REMOVE ALL GENERATED COMMENTS BEFORE SUBMITTING YOUR PULL REQUEST!
+
+class Libmodbus < Formula
+  homepage 'http://libmodbus.org'
+  url 'https://github.com/downloads/stephane/libmodbus/libmodbus-3.0.3.tar.gz'
+  sha1 '28f7dcd418181306dd9e3fc1d409b8e0e963c233'
+
+  def install
+
+    system "./configure", "--prefix=#{prefix}"
+    system "make install"
+  end
+
+  test do
+    # `test do` will create, run in and delete a temporary directory.
+    #
+    # This test will fail and we won't accept that! It's enough to just replace
+    # "false" with the main program this formula installs, but it'd be nice if you
+    # were more thorough. Run the test with `brew test libmodbus`.
+    system "false"
+  end
+end