support global configuration.

[stephenplusplus]

#191
#172

Here we go!

http://stephenplusplus.github.io/gcloud-node/#/docs explains a lot of this for me :)

But, key points:

1. Support global configuration
2. Remove new use from dataset & storage

These changes went hand in hand.

Smaller changes:

1. Using a community extend module
2. Added a "Getting started with gcloud" to the top of the doc's module pages.

[ryanseys]

Other than a few small blips I've addressed in comments, this LGTM.

Would like clarification on how the type of gcloud.datastore and gcloud.storage change depending on whether gcloud is executed with config values or not.

If I call var gcloud = require('gcloud')(); it should be the same thing as var gcloud = require('gcloud'); which is currently not the case. Can this be addressed?

[ryanseys]

Also, docs are 🏀'n

[stephenplusplus]

Note: will need to add special handling of "credentials" vs "keyFIlename" for this case:

vargcloud=require('gcloud')({keyFilename: '/file.json'});vardataset=gcloud.datastore.dataset({credentials: {}});

[stephenplusplus]

Updated the PR to add handling for connection details overriding.

Also updated my gh-pages branch: http://stephenplusplus.github.io/gcloud-node/#/docs