Combine views into a single ddoc

[redgeoff]

As per http://mail-archives.apache.org/mod_mbox/couchdb-user/201712.mbox/%3CD7D02FB1-8761-47BF-96E6-A561EA08FC84%40apache.org%3E, Jan says

Quick comment on one or multiple view(s)-per-ddoc: this is a performance trade-off and not
either one is always correct. But generally, I would recommend grouping all views an app would
need into a single ddoc.

For each ddoc, all docs in a database have to be serialised and shipped to couchjs and the
results are shipped back, that’s the bulk of the work in view indexing. Evaluating a single
map/reduce function is comparatively minuscule, so grouping views in a single ddoc makes that
more efficient.