Add parseStringSync

[mckramer]

Create a sync version of parseString to API to permit calling without a callback. The current implementation is sync due to underlying implementation of SAX parser.

This is a rebased version of #319 by @mrparkers which in turn was an add-on to #241 by @nobodyman. In addition to those changes, this PR:

1. Allows user to specify options to global parseStringSync method as requested here
2. Add additional tests for the parser + global version of the method
3. Adds info to README to describe usage of new methods

Examples:

// Via root API
var result = xml2js.parseStringSync('< ... >', options)

// Via parser
var parser = new xml2js.Parser(options);
var result = parser.parseStringSync('< ... >');

See #241 by @nobodyman
See #319 by @mrparkers

[coveralls]

Coverage increased (+0.1%) to 97.746% when pulling c7df57c on mckramer:parse-string-sync into f8a4d69 on Leonidas-from-XIV:master.

[coveralls]

Coverage increased (+0.1%) to 97.746% when pulling c7df57c on mckramer:parse-string-sync into f8a4d69 on Leonidas-from-XIV:master.

[tiaozi0912]

It would be nice if it could be merged

[RikkiGibson]

👍 to this, there should be no I/O happening in a function called parseString and so see no reason for it to be asynchronous

[lacroixthomas]

+1

[maitriyogin]

any ideas when this can be merged?

[julia-suarez-deel]

Please merge this..

[1mike12]

lol why would this not be merged?

[fkirc]

For a function that is called parseStringSomething, it is strange that there doesn't exist a synchronous version.
After all, all the parsing logic should be naturally synchronous.

Nevertheless, I hope that volunteers will get permission to continue maintenance.

[ErrorBot1122]

@Leonidas-from-XIV Plz merge this... I need sync function because I'm trying converting the parser to "sync" new Parser({async: true}) and parsing returns this mess!!!

{
  comment: '',
  sgmlDecl: '',
  textNode: '',
  tagName: '',
  doctype: '',
  procInstName: '',
  procInstBody: '',
  entity: '',
  attribName: '',
  attribValue: '',
  cdata: '',
  script: '',
  c: '',
  q: '',
  bufferCheckPosition: 65536,
  opt: { trim: false, normalize: false, xmlns: false, lowercase: undefined },
  looseCase: 'toUpperCase',
  tags: [],
  sawRoot: false,
  closedRoot: false,
  closed: false,
  error: null,
  tag: null,
  strict: true,
  noscript: true,
  state: 0,
  strictEntities: undefined,
  ENTITIES: {},
  attribList: [],
  trackPosition: true,
  column: 0,
  line: 0,
  position: 0,
  errThrown: false,
  onerror: [Function],
  onend: [Function],
  ended: false,
  onopentag: [Function],
  onclosetag: [Function],
  ontext: [Function],
  oncdata: [Function]
}

my repo: https://github.com/ErrorBot1122/Roblox-Parser