finish ergonomics

[fpgaminer]

Right now, finish needs to be called on an LzmaWriter to get it to finish compressing/decompressing. This differs from the way a normal Write-like object works, so it's easy to forget and cause weird bugs.

Investigate the suggestion of using Drop to either call finish or panic if finish hasn't been called. BufWriter implements Drop like this: https://static.rust-lang.org/doc/master/src/std/io/buffered.rs.html#501-509

Credits to krdln for the feedback.

[mokasin]

I agree partly. Of course it is cumbersome to call finish and easily forgotten (maybe this should be stated more prominently in the documentation and README). But it has the drawback, that you never will get back the inner Write object. This makes writing multiple framed compressed objects to a Writer more difficult.

[mokasin]

Also the only way to react on errors in Drop is to panic. Which does not seem to be a good general approach.

[Pardoxa]

Maybe you could add a feature "finish_on_drop" or something like that.
That way each user can decide.