add Rscons.clear() class method

lib/rscons.rb

@@ -22,4 +22,13 @@ module Rscons
 
   class BuildError < Exception
   end
+
+  # Remove all generated files
+  def self.clean
+    cache = Cache.new
+    cache.targets.each do |target|
+      FileUtils.rm_f(target)
+    end
+    Cache.clear
+  end
 end

lib/rscons/cache.rb

@@ -132,6 +132,11 @@ module Rscons
       }
     end
 
+    # Return a list of targets that have been built
+    def targets
+      @cache[:targets].keys
+    end
+
     # Private Instance Methods
     private
 

spec/build_tests_spec.rb

@@ -120,6 +120,17 @@ describe Rscons do
     File.exists?('build/two/two.o').should be_true
   end
 
+  it 'cleans built files' do
+    lines = test_dir('build_dir')
+    `./build_dir`.should == "Hello from two()\n"
+    File.exists?('build/one/one.o').should be_true
+    File.exists?('build/two/two.o').should be_true
+    Rscons.clean
+    File.exists?('build/one/one.o').should be_false
+    File.exists?('build/two/two.o').should be_false
+    File.exists?('src/one/one.c').should be_true
+  end
+
   it 'allows Ruby classes as custom builders to be used to construct files' do
     lines = test_dir('custom_builder')
     lines.should == ['CC program.o', 'LD program']