Rely on a calls to an API for spec references rather than bundling the whole ref file.

This pull request changes a number of things.

First, it modifies the codebase to rely on the [specref API](https://github.com/tobie/specref). The main benefit of this change is that it frees the respec project from being redeployed each time a reference is modified or added. The specref API uses continuous integration testing to verify the integrity of the database after a change and automatically redeploys without the need for manual intervention.

Secondly, it removes the reference database from the repository.

Thirdly, and that might be slightly more controversial, it removes the `previousVersions` support for local entries. The specref API handles the expansion of those at the API level (e.g. for [DAHUT-TEST5](http://specref.jit.su/bibrefs?refs=DAHUT-TEST5)) and I thought the use case at the local entries level wasn't that compelling. (Also, I kind of found out about it _after_ having teared it away from the code base and got lazy). @marcoscaceres: I'd love your feedback on this. I can always add it back in if you think there's value to it.