Add promise support to all public functions

[dmihal]

Discussed in #252

[holgerd77]

Whew. What a PR! 👍 🍰 😄

[holgerd77]

@dmihal The Circle tests can be ignored for now, they are not working atm (at least they have to be re-triggered to run through), passing travis is essential.

[dmihal]

@holgerd77 It looks bigger than it is, since it re-indents most of the public API functions.

Here's the diff with whitespace ignored

[holgerd77]

@dmihal Ah, didn’t realize this on first look. 😄

@yann300 Does this PR create any potential problems for remix?

[holgerd77]

@dmihal Ah, tests passing, cool!

[axic]

I don't think it is a good idea to return a promise which will never resolve - that is the case when a callback is passed (e.g. the old-world compatibility mode).

Wouldn't it make sense keeping the old interface unchanged and adding a promise API in front (or the other way around).

Also I'd be supportive internally moving to promises, which is a lot of work, and that would mean that the call back interface would need become the wrapper API.

[holgerd77]

Can't we just put the switch in an if statement to have a more clean implementation with not returning an unresolved promise and at the same time keep the original idea and not have an additional/second API?

VM.prototype._populateCache = function (addresses, cb) {
  self.stateManager.warmCache(addresses, cb)
}

VM.prototype.populateCache = function (addresses, cb) {
  if (!cb) {
    var self = this
    return new Promise(function (resolve, reject) {
      cb = function (err, result) { err ? reject(err) : resolve(result) }
      self._populateCache(addresses, cb)
    })
  } else {
    self._populateCache(addresses, cb)
  }
}

[dmihal]

Going to close this, #273 is a much cleaner change