Add `bin` directory to the default list of packaged files

[Fuco1]

I think the convention is pretty wide spread, all packages that have a binary store it in a bin directory and adding that explicitly complicates things.

I'm pretty sure this wouldn't break anything and it would make packaging simpler. Also it would fix issues like this: cask/cask#395 (comment)

[purcell]

In many cases elisp is part of a larger project, e.g. a language implementation which also has an Emacs major mode. I think blanket inclusion of bin would therefore be the wrong thing to do in the majority of cases.