Finish mechanism for importing mime types

[WebeWizard]

The File Responder should include a big list of common mime types by default.

However, I think the we should be able to pass in a Vec<(&str,&str)> or... [(&str,&str); 20] to replace the default with a list. If we assume the provided list is smaller than the default, it will perform better. (Imagine a folder of thumbnails where we KNOW the only file type present is .png)

Need to compare Vec vs array performance. What about crates like StackVec?

[WebeWizard]

Also imagine a case where a folder can contain many different types, but we've measured that some types get requested much more frequently than others. If we position those at the beginning of the Vec/Array, the mime type lookup will perform much faster for those cases.

[WebeWizard]

What about a hidden .config file or something that can be read from to provide folder/child specific mime types?