Add examples to the DS.Errors api docs.
Fix validation comments for

- Api docs included comments on failing client-side validation
- DS.model doesn't have client side validation
- Only code that sets errors and changes  is a result
  of an invalid response from server
[DOC beta] Clarify adapter settings with ActiveModel::Serializers
Import InvalidError instead of looking at global DS
Merge pull request #1891 from Kerrick/remove-reliance-on-global-ds

Import InvalidError instead of looking at global DS
[DOC] `bower install` is part of `npm install`, removing it from README
Merge pull request #1899 from bantic/update-readme

[DOC] `bower install` is part of `npm install`, removing it from README
Merge pull request #1881 from bmac/errors-examples

Add examples to the DS.Errors api docs.
Merge pull request #1887 from pixelhandler/active-model-adapter-docs-settings

[DOC] Clarify adapter settings with ActiveModel::Serializers
Merge pull request #1885 from pixelhandler/validation-comments-correction

[DOC] Fix validation comments for DS.Model#isValid