Support static metadata

[zemuldo]

PR has support for static metadata that can be put while encoding a message and can be retrieved when decoding the message.

GitHub Issue: https://github.com/zemuldo/iso_8583/issues/76

const Main = require('iso_8583');
let data = {
    0: '0100',
    2: '4761739001010119',
    3: '000000',
    4: '000000005000',
    7: '0911131411',
    12: '131411',
    13: '0911',
    14: '2212',
    18: '4111',
    22: '051',
    23: '001',
    25: '00',
    26: '12',
    32: '423935',
    33: '111111111',
    35: '4761739001010119D22122011758928889',
    41: '12345678',
    42: 'MOTITILL_000001',
    43: 'My Termianl Business                    ',
    49: '404',
    52: '7434F67813BAE545',
    56: '1510',
    123: '91010151134C101',
    127: '000000800000000001927E1E5F7C0000000000000000500000000000000014A00000000310105C000128FF0061F379D43D5AEEBC8002800000000000000001E0302031F000203001406010A03A09000008CE0D0C840421028004880040417091180000014760BAC24959',
  };

 const staticMeta = 'ISO70100000';
 const isopack = new Main(data);
 isopack.setMetadata(staticMeta);
// Create buffer that has static data
 const buffer = isopack.getBufferMessage();

 console.log(buffer)
 console.log(buffer.byteLength)
 console.log(buffer.toString())
 console.log("------------")

 const json = new Main().setMetadata(staticMeta).getIsoJSON(buffer,{})

 console.log(json)