add C extension

ext/svi/extconf.rb

@@ -0,0 +1,3 @@
+require "mkmf"
+
+create_makefile "svi/svi"

ext/svi/svi.c

@@ -0,0 +1,5 @@
+#include <ruby.h>
+
+void Init_svi(void)
+{
+}

lib/svi.rb

@@ -1,6 +1,7 @@
 require_relative "svi/cli"
 require_relative "svi/svn_runner"
 require_relative "svi/version"
+require "svi/svi"
 
 module Svi
   # Your code goes here...

svi.gemspec

@@ -25,6 +25,7 @@ Gem::Specification.new do |spec|
   spec.files         = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.extensions    = %w[ext/svi/extconf.rb]
   spec.require_paths = ["lib"]
 
   spec.add_development_dependency "bundler", "~> 1.10"