expose the Input trait

[njskalski]

I wanted to wire "Input" trait to ropey::Rope, but I get regex::prog is "private module". I can write patch myself, this is rather a question: is there a reason this is not enabled by default or just nobody needed it so far?

[BurntSushi]

The issue title here seems totally disconnected from the actual substance of the request. I've renamed the title...

Well, yes, there is a reason. It's not part of the public API and never will be.

For executing regexes on discontiguous text, see: #425

For longer term plans, see: #656

[BurntSushi]

Closing this because the Input trait will actually be removed at some point and there really aren't enough details in this request to make it actionable. #425 is probably a better general ticket if the use case is to indeed do a regex search on discontiguous text.