(pouchdb/pouchdb#3056) - _changes with POST

`_changes` needs to accept POST as well as GET
because of doc_ids.
(#130) - Update sendfile to sendFile

The lowercase version of sendfile has been deprecated in favor of the upper case version by express. See, for example, [here](http://stackoverflow.com/questions/26202150/express-js-error-express-deprecated-res-sendfile-use-res-sendfile-instead)
(#132) - Get rid of 'dbs' by using allDbs() more
(#16) - Split out routes into separate files