Bug/connection timeouts

This pull request fixes #2 by checking maintaining a connection state with an expiration for the outstanding jsforce session. This state is checked with each request to the adapter and if the connection life has exceeded the max age specified in the adapter config then a new connection will be spawned. 

To test this you'll need to checkout this branch and link it to your sails project. For example:
```sh
cd ~/dev/sails-forcedotcom               
git pull
git fetch
git checkout bug/connection-timeouts
sudo npm link
cd ~/dev/schooner
npm link sails-forcedotcom
```