getAsync call options.error once

In error callback of getAsync call options.once. If there where no models created, just refreshed options.error was never called.
Merge pull request #473 from sventschui/master

getAsync call options.error once
Fix expected outcome on number of error callbacks triggered by getAsync
Update old comment referring to `relations` as a function. Ref #475
Allowed Chrome to optimize Collection.set and RelationalModel.extend.
Perhaps will help #480?
getAsync: avoid building 'stub' models whenever possible (because the collection can create a url when given a set of ids).
Fix options name in documentation: `options.update` to `options.merge`
When a relation doesn't specify a `relatedModel`, default to being self-referential.
getAsync: set proper option for Backbone 1.1 ('add' instead of 'update')
Add missing semicolon in documentation
Linkify the reverseRelation `type`, and format it as code.

Since we are talking about keys 'key', 'relatedModel', and 'type' in
reverseRelation, we should make them all consistent.
Merge pull request #496 from rwong48/link-and-format-type

Linkify the reverseRelation `type`, and format it as code.
Merge pull request #492 from Spy-Seth/patch-1

Fix options name in documentation: `options.update` to `options.merge`
Merge pull request #495 from rwong48/add-missing-semicolon-in-documentation

Add missing semicolon in documentation
Update version numbers to 0.9.0
Merge branch 'coll-set-optimizations' of https://github.com/AsymmetricVentures/Backbone-relational into AsymmetricVentures-coll-set-optimizations
Pick a few optimizations, convert `getReverseRelations` to for loops (seems to be a hotspot).
Merge branch 'AsymmetricVentures-coll-set-optimizations'
Update backbone/underscore version number
Merge branch 'master' of github.com:PaulUithol/Backbone-relational