Remove BuildTarget, Builder#create_build_target, and Builder#setup - close #90

spec/rscons/builder_spec.rb

@@ -2,7 +2,7 @@ module Rscons
   describe Builder do
     describe "#run" do
       it "raises an error if called directly and not through a subclass" do
-        expect{subject.run({})}.to raise_error /This method must be overridden in a subclass/
+        expect{Builder.new({}).run({})}.to raise_error /This method must be overridden in a subclass/
       end
     end
   end

spec/rscons/builders/simple_builder_spec.rb

@@ -4,7 +4,7 @@ module Rscons
       let(:env) {Environment.new}
 
       it "should create a new builder with the given action" do
-        builder = Rscons::Builders::SimpleBuilder.new { 0x1234 }
+        builder = Rscons::Builders::SimpleBuilder.new({}) { 0x1234 }
         expect(builder.run(1,2,3,4,5)).to eq(0x1234)
       end
     end