Base64 encoded pdf content in API request

[pofider]

I started to use this format for sending base64 encoded content instead of the referenced asset.

https://github.com/jsreport/jsreport-pdf-sign/blob/master/test/pdfSignTest.js#L116

reporter.render({
      template: {
        content: 'Hello',
        engine: 'none',
        recipe: 'chrome-pdf',
        pdfSign: {
          certificateAsset: {
            content: fs.readFileSync(path.join(__dirname, 'certificate.p12')).toString('base64'),
            encoding: 'base64',         
          }
        }
 })

The same is here in the docxtemplater.
It sounds this will be occurring quite often in our API so it would be better to unite it.

@bjrmatos What you think?

[bjrmatos]

done as part of 0.2.0 and the encoding property is required instead of setting some default