Allow passing customHash in fingerprint options

[chnn]

This adds a customHash option that can be passed to the fingerprint configuration:

var app = new EmberApp({
  fingerprint: {
    enabled: true,
    customHash: 'custom123'
  }
});

The result is that fingerprinted files will use the customHash string instead of a MD5 hash of the file. (e.g. "assets/vendor-5429f75166356b28c3e42dd401abaf36.js" becomes "assets/vendor-custom123.js").

The motivation behind this is that it's difficult to get the names of fingerprinted files if you aren't using the ember-cli generated dist/index.html file. By using customHash, you can set the fingerprint to be something like the current commit's SHA if you are working in a git repo or a version number from a package.json file. Those are easier to predict and setup in a non ember-cli generated index.html template elsewhere.

It relies on some new functionality released in broccoli-asset-rev 0.0.6.

[chnn]

anyone?

[stefanpenner]

@Chenn can you rebase? Also, we are working hard on a proper plugin api with configuration. Some progress has been made, hopefully with you input we can move this to that.

[chnn]

rebase into master? I already squashed the commits.

I'd be happy to take a stab at moving the whole fingerprinting functionality to a plugin. Would that be preferred to this?

[stefanpenner]

@Chenn rebase to master, as it no longer merges cleanly

[chnn]

ok, should merge cleanly now.

[stefanpenner]

no longer merges cleanly.

[chnn]

@stefanpenner it should now.

[raycohen]

let's get this handy feature documented in http://www.ember-cli.com/user-guide/#fingerprinting-and-cdn-urls