More flexible file selection from FTP

[avit]

Currently it's hard to get the mtime of files on the server without querying them individually (it's a limitation of the FTP protocol) and the ftp.list command just gives us a list of unstructured strings in ls -l format.

The net-ftp-list gem would allow us to easily parse the output of ftp.list instead of just getting the filenames from ftp.nlst: this means we could select files on name or mtime criteria.

We should use this to expose a client.search method for selecting files similar to Stockboy::Providers::IMAP.

[markjlorenz]

@avit It's been while since you opened this. Before I start implementing I just wanted to check, do you still think it's a good feature?

[avit]

I haven't had time to start on it yet, but I think it would be a good idea. If you want to add it, a pull request would be very welcome!