zsh completion: enhance store navigation

[Wouter]

Hi all,

I like pass very much and the zsh completions make navigating the store 
quite easy.

There is however something I'd like improved. I have my passwords stored 
hierarchically and currently there are two drawbacks to how the 
completion works:

- First, 'directories' that are being completed do not include a 
trailing slash, forcing me to type those manually which I think is an 
unnecessary distraction.

- Second, I would like the option to complete only items at the current 
'directory' level.
   So if I have 'accounts/amazon.com', 'accounts/devel/github.com' and 
'accounts/devel/bitbucket.com', I'd like `pass accounts/<TAB>` to return 
'accounts/amazon.com' and 'accounts/devel' as results.
   Especially at the root level this would allow for far easier 
completion of directories (currently I'm getting an unusably long list 
containing *all* passwords).

I'm curious to know what others think about these changes. If I find the 
time I could try implementing them myself.

Kind regards,
Wouter