Microfiber 13.11

Added three new experimental Database methods:

  * `Database.iter_all_docs(chunksize=50)`

  * `Database.iter_view(design, view, key, chunksize=50)`

  * `Database.delete_many(docs)`

Note that none of these methods are API stable yet, so use them at your own risk!

The first two methods address the tricky but important pattern of iterating through a set of docs some number of docs at a time, but without any repeating doc IDs or unexpected doc ID gaps. As currently CouchDB doesn't allow you to specify a non-inclusive *startkey_docid*, iterating this way is rather fragile and is very easy to get wrong (eg, it's easy to produce an infinite loop). Although this approach is difficult to implement correctly, it's far superior to stepping through results using the *skip* query parameter.

The first two methods represent an extremely frequent pattern in Dmedia, so it was time to bite the bullet and add them to Microfiber.

The last method isn't anything special, but it is handy and rounds out our set of `Database.verb_many()` methods. This method would often be helpful in Dmedia unit tests, which is why it was added.

`Database.delete_many()` simply sets `doc['_deleted'] = True` for all docs, and then passes them to `Database.save_many()`.