Add .pick() and .omit() methods

[dmarcelino]

This PR is the same as #509, but targeting 0.11, props to @jasonsims. Please check #509 for the full discussion.

Original message:

This PR adds the ability to apply projections to waterline queries. It's an extension of the work accomplished in #162 by adding flexibility for how selection arguments are supplied as well as exclusions via .omit(). With this change, the adapters will always receive a standardized selection criteria object which they can process as needed for their specific query language. Here's an example of this object:

// User.find().pick('name', 'age').exec(cb);
{ where: null, pick: { name: 1, age: 1 } }

// User.find().omit('name', 'age').exec(cb);
{ where: null, omit: { name: 0, age: 0 } }

Usage examples:

// Include only 
User.find().pick('name', 'age').exec(cb);
User.find().pick(['name', 'age']).exec(cb);
User.find().pick({name: 1, age: 1}).exec(cb);

// Exclusion
User.find().omit('name', 'age').exec(cb);
User.find().omit(['name', 'age']).exec(cb);
User.find().omit({name: 0, age: 0}).exec(cb);

fixes #73

cc: @clarkorz, @mikermcneil, @mdunisch, @particlebanana, @sskyy, @devinivy, @tjwebb

[dmarcelino]

#73 actually asks for a .select() method so we should probably follow @devinivy's suggestion on #509 (comment):

I think pick and select should be aliases.

Any volunteers for this?

[tjwebb]

re: http://stackoverflow.com/a/29769995/291180

@dmarcelino would you mind adding a quick sentence or two in the docs about how the select criteria works? I think I didn't know this feature existed either :)

[dmarcelino]

@tjwebb, I can't believe you didn't know about it... to be honest I don't remember how I found out it existed. Sure, I'll look into adding it.

[tjwebb]

to be honest I don't remember how I found out it existed. Sure, I'll look into adding it.

Yea I sort of knew about it, but I've never used it and didn't really know the API. Is it unit tested?

[dmarcelino]

I don't think it is, there are some tests that use it (quick search) but no particular unit test to explicitly test it.

[alexlenail]

Why isn't this a feature yet?

[weyert]

Any news on this?

[randallmeeker]

closed w/o comment?

[chacliff]

personally i think that this should be structured just like mongo structures it... if your going to use "select" or "pick"... not omit it should just be { field: 0 || 1 }, where 0 is to omit, and 1 is to include. by default if no selection is made everything is included. by default if a field is marked with 1 ID is still included unless explicitly marked 0.