Overview.html should only be forced if not in the list

[darobin]

Currently the first line of the manifest is always turned into Overview.html. In some cases it might be that Overview.html is listed elsewhere in the manifest; when that happens the first line should be left as is.

Of course it's possible for manifest generators to work around this, but if for instances they're doing things like listing all files in a directory it'll require special code.

[astorije]

Tagging that as an enhancement, since it's a bug-feature by design :-)

#111 will solve that when implemented. If it takes too long to get started and released, I'll make a quick fix (just because it's you :heart:) but I must admit I have bigger priorities in my plate right now. Stay tuned.