Remove info on how to enable feature flags After Loading Ember.

Not all feature flags work when enabling them after loading Ember e.g.
string-humanize.

This is really misleading, making people believe they are doing
something wrong. In order to avoid that we should encourage people to
use the `ENV` object and enable them always before loading Ember.
Merge pull request #1039 from abuiles/edit_feature_flags_details

Remove info on how to enable feature flags After Loading Ember.
Fixed code markup
Merge pull request #1041 from koorgoo/patch-1

API docs: fixed code markup
Customizing URL prefix now matches api docs
Updated Meetup Assets page
Merge pull request #1043 from jgill/master

Customizing URL prefix now matches api docs
Fix docs to current stable versions.
Add 1.2.0-beta.3 to /build fixtures.
Merge pull request #1044 from rjackson/update_fixtures_for_1-2-0-beta-3

Add 1.2.0-beta.3 to /build fixtures.
use latest release version
Merge pull request #1045 from zigomir/patch-1

use latest release version
No need to set the variant with ember-rails 0.14.
Allow newer ember_source versions.
Merge pull request #1048 from rjackson/update_template

Fixup edge_template.rb.
adding high res assets
Merge pull request #1049 from twokul/retina-assets

Adding high resolution assets for rMBP
{{render}} arg should be in quotes
{{partial}} arg should also be in quotes