Started implementation of the simple backend.

It's a document store and backend all in one. Should be more reliable than the nedb backend. Not finished or tested yet, though.
Finished initial implementation of simple backend; no testing yet.
Exposed SimpleBackend.
Tested and fixed issues with SimpleBackend.

Should be working now; expanded the example to test AutoID fields.
Added support for a 'find all' style query.
Fixed an issue with removing, and several other minor issues.
Added write rate-limiting.

Also changed 'doc' to 'docs' in find, since the general case is multiple documents.
Fixed a few minor issues.

 - Switched the event registration for `initialize` on collections to `once`, not `on`.
 - Fixed a race condition where multiple instances of a collection could be created before the first collection finished initializing.
 - Fixed double-call of a callback in the event of an error condition in find.
Corrected several non-strict comparisons against undefined, unnecessary assignments to undefined, a missing semicolon, and a typo, in the simple backend.
Made test discovery recursive.
Improved error reporting in _writeToDisk.
Corrected config functionality in SimpleBackend.
Added dependency on mkdirp in order to create DB root directories as needed.
Got gzip support closer to working, and improved error reporting.
Added tests for the simple DB backend.
fixed gzip support.
Merge pull request #7 from Morgul/feature-ccase-simplebackend

Implemented Simple Backend