Emit progress event during file download + delete file on remote server

[dbaikov]

Hi folks,

This adds event to monitor file transfer progress for file download.
Change is based on https://github.com/freeall/progress-stream package

related issues #43 #57

Example:

var pretty = require('prettysize');
var prettySeconds = require('pretty-seconds');

client.download(src, dest, callback)
self.client.on('progress', function (progress) {
    console.log(Math.floor(progress.percentage) + ' %');
    console.log(pretty(progress.speed) + '/sec');
    console.log(prettySeconds(progress.eta));
});

5 %
3.4 MB/sec
1 minute and 35 seconds

Also this adds unlink method to delete file on remote server

client.unlink(filename, callback) -> callback(err)

[scotthovestadt]

+1

[francois-travais]

+1

[popomore]

Should listen error event on ps.

[popomore]

Can you rebase it?

[hkeio]

+1

[lepture]

@dbaikov can you rebase it?