Implemented SimpleBuilder and updated Environment#add_builder method to support it

spec/rscons/builders/simple_builder_spec.rb

@@ -0,0 +1,19 @@
+module Rscons
+  module Builders
+    describe SimpleBuilder do
+      let(:env) {Environment.new}
+
+      it "should create a new builder with the given name (as a symbol) and action" do
+        builder = Rscons::Builders::SimpleBuilder.new(:Foo) { 0x1234 }
+        expect(builder.name).to eq("Foo")
+        expect(builder.run(1,2,3,4,5)).to eq(0x1234)
+      end
+
+      it "should create a new builder with the given name (as a string) and action" do
+        builder = Rscons::Builders::SimpleBuilder.new("Foo") { 0x1234 }
+        expect(builder.name).to eq("Foo")
+        expect(builder.run(1,2,3,4,5)).to eq(0x1234)
+      end
+    end
+  end
+end

spec/rscons/environment_spec.rb

@@ -72,6 +72,13 @@ module Rscons
         env.add_builder(Rscons::Builders::Object.new)
         expect(env.builders.keys).to eq ["Object"]
       end
+
+      it "adds a new simple builder to the list of builders" do
+        env = Environment.new(exclude_builders: true)
+        expect(env.builders.keys).to eq []
+        env.add_builder(:Foo) {}
+        expect(env.builders.keys).to eq ["Foo"]
+      end
     end
 
     describe "#get_build_fname" do