feat(): support angular-1.2 ngResource

BREAKING CHANGES:

- Angular 1.0.x and 1.1.x are no longer tested, but still should
  theoretically be supported.
release(): v1.5.0
chore: Update README
feat(promiseTracker): add `activationDelay` option

`activationDelay` `{Number}` - Number of milliseconds that an added
promise needs to be pending before this tracker is active.

Usage example: You have some http calls that sometimes return too
quickly for a loading spinner to look good. You only want to show the
tracker if a promise is pending for over 500ms.

You put `{activationDelay: 500}` in options.
chore: update README
chore: add docs to README
Update README.md
chore: add plunkr for basic demo to README
release(): v1.5.1
chore(README): update incorrect event name
chore(README): update table of contents
chore(README): shorten introduction to one sentence
feat(promiseTracker): add register() and deregister() methods

BREAKING CHANGE:

A promiseTracker instance can no longer be created with the
`promiseTracker` function, it is a getter only now.

To migrate your code, change the following:

```js
var newTracker = promiseTracker('newTracker', options);
//..later
var tracker = promiseTracker('newTracker');
```

To:

```js
var newTracker = promiseTracker.register('newTracker', options);
//..later
var tracker = promiseTracker('newTracker');
```

Check the [project
README](http://github.com/ajoslin/angular-promise-tracker/tree/master/README.md)
for more details about this change.
feat(promiseTracker): remove events system

BREAKING CHANGE:

The events system has been removed.  That means you can no longer do
`.on()` and `.off()`.  In essence, events were a poor way of doing
'hooks' on promises.  See [this
issue](https://github.com/ajoslin/angular-promise-tracker/issues/37) for
more information.

[Open an
issue of your own](https://github.com/ajoslin/angular-promise-tracker/issues) if you
were using events and need help migrating to use anotehr method.

Check [the
README](https://github.com/ajoslin/angular-promise-tracker/tree/master/README.md)
for details on the current API for promiseTracker.
release(): v2.0.0-beta1
chore(): Update README.md
chore(CHANGELOG): clarify .register() change
chore(README): fix typo
chore(): add travis testing
release(): v2.0.0-beta2