Ability to delete custom post type posts by categories

Earlier, deleting posts by category delete posts only from the 'post'
post-type. This commit adds an option to choose post-type in addition to
selecting category.

Fix #30
Ability to delete custom post type posts by taxonomy

Earlier, deleting posts by custom taxonomy delete posts only from the
'post' post-type. This commit adds an option to choose post-type in
addition to selecting custom taxonomy.

Fix #37
Fix link to "Custom Field" addon
Bumpup version to v4.3 for release
Regenerate pot file for v4.3