Added a few capabilities to ERM

First, I added the ability to query the count: 

Ex: ...api/v1/todos/count/?done=true   

returns: 
  { 'count': INT } 

// Uses 'buildQuery' so other functionality, like regex, is still intact. 

Next, I added an 'exclude' option and a /?select= option to the API.  

'exclude' is setup during initialization: 

Example: 
  restify.serve(app, ToDoModel, { 
		exclude: 'text,done' // this fields cannot be returned from the API, period. 
  });
In contrast, the /?select= option is appended to the URL and is not capable of overriding the 'exclude' option (if it exists).  So we can exclude usernames/passwords/sensitive-data.  /?select= works like this: 

1) Tell it which fields you want back: /?select=fieldname1,fieldname2,fieldname3

It was my intention to make a defaultSelect as you might see in my commit history, however I guess Mongoose does not support the combination of inclusion/exclusion within the model.#select().