Explain how to define custom test helpers

This update proposes a way to use Ember's built in helper registration.

I apologise if I've poorly grasped any of the concepts around modularization / ember-cli, but hopefully this is a good first stab at it.  I've tested the 'style' I've proposed and it does work, but if there's a more idiomatic way, I'd love to hear :)
Doh!  Intermediate variable not needed!
Add notes about .jshintrc
Update docs to mention using `podModulePrefix` in test resolver.
[DOC] Using canary build instead of release
Add import statements to examples
Merge pull request #1244 from joostdevries/gh-pages

Add import statements to examples
Merge pull request #1242 from pixelhandler/gh-pages

[DOC] Using canary build instead of release
Fixed accidental comment
Added missing import statements
Merge pull request #1245 from joostdevries/gh-pages

Corrected import statements in examples
Merge pull request #1050 from WMeldon/pod-prefix-docs

Update docs to mention using `podModulePrefix` in test resolver.
Merge pull request #965 from mfeckie/patch-2

Explain how to define custom test helpers
Update description.html
Update description.html

replace em dash with dash dash
Update AMD import

update code example according to #1121
Merge pull request #1269 from flecno/patch-1

Update description.html
squashes 7 commits
Merge pull request #1038 from kavitshah8/gh-pages

adds an example for css asset compilation