Add PackageManifest classes for ruby manifests

Creates PackageManifest class for various ruby manifests
and overrides the methods for detection and PackageManifest creation.

Signed-off-by: Ayan Sinha Mahapatra <ayansmahapatra@gmail.com>

Author: AyanSinhaMahapatra

src/packagedcode/__init__.py

@@ -67,7 +67,10 @@
     bower.BowerJSON,
     freebsd.FreeBSDCompactManifest,
     models.CpanModule,
-    rubygems.RubyGem,
+    rubygems.RubyGemArchive,
+    rubygems.RubyGemArchiveExtracted,
+    rubygems.RubyGemSpec,
+    rubygems.RubyGemfileLock,
     models.AndroidApp,
     models.AndroidLibrary,
     models.MozillaExtension,