[#180] Separate logical blocks: vars init
[#180] Separate logical blocks: vars init

1. Rename vars
  - source -> self.source
  - dest -> self.dest
  - rev -> self.rev
  - dburl -> self.dburl
  - docid -> self.docid
  - path -> self.path
  - doc -> self.doc
  - manifest -> self.manifest
  - signatures -> self.signatures
  - objects -> self.objects

2. logical block: `init_path`

3. logical block: `init_metadata`

couchapp/couchapp,couchapp/couchapp,couchapp/couchapp,couchapp/couchapp