`salesforce` Provide direct helper function for file uploads

Clients occasionally need to send files to Salesforce—the use case would be to fetch a file from X or Y SFTP server and then load it to SF. Consider, do we stream? How do we avoid saving the file to state between jobs? How do we minimize the memory usage of the NodeVM?

This looks good: https://github.com/jsforce/jsforce/issues/43#issuecomment-80522041 . Should we provide a helper function to wrap this up for the adaptor?

'use strict';
var fileOnServer = '/home/ubuntu/myuploaddir/randomfile/randomimage.jpg',
    fileName = 'MyRandomImage.jpg',
    fileType = 'image/jpeg';

fs.readFile(fileOnServer, function (err, filedata) {
    if (err){
        console.error(err);
    }
    else{
        var base64data = new Buffer(filedata).toString('base64');
        jsForceConn.sobject('Attachment').create({ 
                ParentId: 'mysalesforceContactID',
                Name : fileName,
                Body: base64data,
                ContentType : fileType,  
            }, 
            function(err, uploadedAttachment) {
                console.log(err,uploadedAttachment);
        });
}
});

No repository file or test is named. Start with the Salesforce Attachment upload example in the issue and the linked jsforce discussion, then determine the adaptor entry point and how streaming, job state, and NodeVM memory should be handled. Done means a defined helper interface and tests covering the intended upload behavior and resource constraints.