Fix incorrect documentation for isError.

If the server returns a validation error, then isError is not set to true.
Add a better transform example
[DOC] Fix docs for method signature of extractSingle, extractArray
Fixes a typo in the documentation of the serializeAttribute method of json_serializer.js
incase jQuery.ajax returns a null or undefined jqXHR
Remove incorrect semicolon from pathForType example.
Also changed the example to use .extend instead of reopen
Merge pull request #1918 from bmac/fix-pathfortype

Remove incorrect semicolon from pathForType example.
Merge pull request #1898 from bantic/extract-single-array-docfix

[DOC] Fix docs for method signature of extractSingle, extractArray
Merge pull request #1902 from abrinkman/master

Fixes a method documentation typo.
Merge pull request #1897 from alexspeller/fix-poor-transform-example

Add a better transform example
Merge pull request #1858 from jimmay5469/patch-1

Fix incorrect documentation for model.isError