Module generator finishes for partially existing files

This resolves #219. When generating a new module, if all the files to
generate already exist then it fails as before. If some of the files
already exist, then the files that need to be created are created. Any
existing files are not changed.

Also added a bunch of tests for this feature via rspec. Run them from
the test folder with `rake spec`.

test/rakefile

@@ -10,9 +10,11 @@ $verbose = false
 require 'rake'
 require 'rake/clean'
 require UNITY_ROOT + 'rakefile_helper'
+require 'rspec/core/rake_task'
 
 TEMP_DIRS = [
-	File.join(UNITY_ROOT, 'build')
+	File.join(UNITY_ROOT, 'build'),
+	File.join(UNITY_ROOT, 'sandbox')
 ]
 
 TEMP_DIRS.each do |dir|
@@ -40,6 +42,11 @@ task :scripts => [:prepare_for_tests] do
   end
 end
 
+desc "Run all rspecs"
+RSpec::Core::RakeTask.new(:spec) do |t|
+  t.pattern = 'spec/**/*_spec.rb'
+end
+
 desc "Generate test summary"
 task :summary do
   report_summary