Fixed: headers were incorrect or missing.
Fixed: converting xib with Autolayout gave confusing error message.

Previously, attempting to nib2cib a xib with autolayout would give an error message that there was no class to archive NSLayoutConstraint, which was meaningless to most people.

Now an error message that says exactly why it failed and how to fix it is given.
Fixed: deleted xib or cib files were not processed correctly.

Now, deleting a xib file will delete its corresponding cib. Deleting the cib will mark its corresponding xib for updating.
Docs: updated XCC help.