Chicken milanese with fries

Oh, this with this release the 0.9.0 starts being the advices version to be used.

Many things have improved, many bugs were fixed. Some highlights:

• [FEATURE] Fastboot support!! The component now should render perfectly in Fastboot Mode
• [FEATURE] Proper Accesibility!! Lots of roles and aria-* tags have been added to make the component
  friendly, according with the guidelines in the RFC
• [FEATURE] $ember-power-select-line-height variable can have units now.
• [FEATURE] The .ember-power-select-option elements added to wrap the noMatchesMessage and the searchMessage have special classes to help styling them (ember-power-select-option--no-matches-message & ember-power-select-option--search-message)
• [BREAKING CHANGE] The ember-power-select-options--nested class is not used anymore. Now nested groups
  have role=group, and the top-most one has role=listbox.
• [BREAKING CHANGE] The *--open class on the .ember-power-select div has been removed. Now styles
  target [aria-expanded=true/false], and it applies to the trigger, not to the top-most div.
  People explicitly targeting this class in they styles will need to update.
• [BREAKING CHANGE] Warning. Classes ending in --disabled, --highlighted and --selected have been
  replaced by aria attributes [aria-disabled="true"], [aria-current="true"] and [aria-selected="true"]
  respectively. Those attributes are needed for a11y and the recomendation is to style based on them
  instead of classes.
  Styles have been updated accordingly, so people using them and customizing the appearance using the
  sass variables won't notice anything, but people that relied on those classes for overriding styles
  will have to update them.
• [BUGFIX] When the component received a promise as options and also a search action, clearing
  the search must show the content of that promise.
• [BUGFIX] Single selects without searchbox can be focused normally. Fixed updating ember-basic-dropdown.
  Ember basic dropdown was calling preventDefault on the mousedown event to prevent the user to
  select text when moving the mouse between the mouseup and the mousedown. Now the event is not defaultPrevented,
  it uses another technique.
• [BUGFIX] When the list of options is empty but the component is given a search action, it should
  not show the No results found until the user actually performs a search and there and it comes
  empty.

The most relevan part about breaking changes is many styles that used to target classes, like ember-power-select-option--disabled will now target aria-* attributes, like aria-disabled=true. People using the default styles or customizing them using the sass variables will be fine. People targeting those clases will have to change their styles to target the proper attributes.

This is annoying but is necessary in order to enforce good practices in accessibility. People that want to reuse the default styles will have to add the proper a11y attributes, resulting in a ecosystem of addons based on ember-power-select that are accesible by default.