2.1 API not backwards compatible with 2.0 executable

[tresf]

Quoting an email from a beta user:

We're trying to integrate qz-tray.js@version 2.1.0 [... with the ...] Tray 2.0 executable for receipt printing. All the characters are getting printed, but control commands such as Bold, Double font, etc... are not working.

We're using the code like this, ex: for Bold ON

function chr(i) {
    return String.fromCharCode(i);
} 
var cmd_on = chr(27)+ chr(33) + chr(8);
var cmd_off = chr(27)+ chr(33) + chr(0);
var printData = [
   { type: 'raw', format:'plain', data: cmd_on },
   { type: 'raw', format:'plain', data: "Text to print" },
   { type: 'raw', format:'plain', data: cmd_off) }
];

2.1 has modified the API a bit... namely, 2.1 uses "type", "format" and "flavor" parameters as explained here: https://qz.io/wiki/2.1-Raw-Printing#escpos.

[akberenz]

Ready to test under bba7e5e on compat branch.

Also possibly related to the user's problem and worth noting:
That sample code uses format:'plain' which only exists as such in 2.0's data format. Using that with the 2.1 javascript has undefined results (since 2.1 js expects 2.1 data format, regardless of what version executable its talking to).
This change will make it appear to work correctly, but that is only because of the lossy conversion process required to support 2.0's data format coupled with the default format for the 'raw' type.

[tresf]

@bberenz can we shim in base64 raw support as well? The 2.1 API allows this to be provided as a flavor, but back in 2.0 it was hacked into the URL.

[akberenz]

Base64 changes available under f27a562

[tresf]

Closed via #348.