Adding a manifest option

[piyushchauhan2011]

It would be nice to have a manifest option there to output a manifest.json file with all the mapping of source files without fingerprint to destination files with fingerprint. We use require.js with require.css and it's required to get the fingerprinted file name to load on-demand assets according to requirements.

Thanks.

[jabes]

For such a popular repo, I'm surprised this doesn't exist yet. You have the option of using grunt-usemin and grunt-filerev or maybe grunt-hashmap?