Replaced Pongo instances with MongoClient.

 - implemented callback buffering
 - first step to remove Pongo as dependency
 - other improvements in storing options
Use Mongo objectid instead of Pongo
Removed Pongo as dependency. Added MongoDB. Stable versions
Removed Pongo dependency for ObjectIds
Added missing semicolons. Updated syntax
Lot of syntax fixes

 - beautified js files
 - added missing semicolons
 - deleted unnecesary semicolons
 - double quotes
 - renamed some variables
Regenerated package.json. Added test command and other fields
Cache server objects

Also added the tests for server object caching. However, they fail because of an error thrown from Mongo driver.
Client object cache
args instead of arguments
Removed debugger lines
Improved callback calling
Default options for server
Merge pull request #27 from adioo/mongoclient

Replaced Pongo instances with MongoClient.