feat: add `make rc` target. Requires `COUCH_RC` env var set to an int.
feat: add `make rc` target. Requires `COUCH_RC` env var set to an int.

Example:

    ./configure
    COUCH_RC=2 make rc # produces `apache-couchdb-2.0.0-RC2.tar.gz

Extracts into a directory called `apache-couchdb-2.0.0-RC2`.

Set `COUCH_RC=3` for RC3 and so on.

Bails with an hopefully helpful error message if `COUCH_RC` is not set.

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb