- couchbase module is now a constructor. connect() api is removed.
- calling the constructor with a configuration settings, return a couchbase
  bucket instance.
- added default configuration.
- constants like, error-codes and observer-status can be accessed through
  bucket instance.

bucket module is partially changed - especially for set,replace,add,touch
public-apis.

- general idea is to do parameter validation only when `debug` is configured
  as true.
- and, console logging is done only when both `debug` and `log` is configured
  as true.

Additionally,

.on("error", callback) is not done by couchnode, applications using couchnode
can optionally subscribe to connection errors.

.on("connect", callback) is removed entirely, I am not sure why this needed.
Added a test case 00-version.js and modified existing test case 01-set.js to
suite the latest version of couchnode (refer to previous commit).
Added an apidoc. Just getting it started.