`unwrap` has a panicky connotation, recommend `into_inner` instead

[apoelstra]

Feel free to close as this is just whining about the API, but I think the unwrap methods should be renamed on the Cursor types, and perhaps elsewhere. See for example

https://docs.rs/rincon_session/0.1.0/rincon_session/client/struct.Cursor.html#method.unwrap

The issue is that unwrap on Result and Option may cause the thread to panic, so readers of code may have an aversion to any functions with this name because they may mistake it for a potential "panic on error".

A better name would be into_inner, such as used by https://doc.rust-lang.org/std/io/struct.Cursor.html#method.into_inner