Simplify rubygems version string.

Rubygems only supports letters, numbers, and period as part of the
version string. This uses the new structure implemented in
https://github.com/emberjs/ember.js/commit/3d8d23af6d9f1387ee37d9588bd567704730ee21
and simplifies the generated rubygems_version_string for non-published
versions.
[BUGFIX beta] reduceComputed handle out of range indexes.

Make `ReduceComputedProperty`'s `DependentArrayObserver` respect out of range
indexes the same was `[].splice` and `MutableArray.replace` do, namely:

- idx >= length is treated as removing no items and pushing new items and
- idx < 0 && idx < |length| is treated as a 1-based index from the right and
- idx <= |length| is treated as 0.

Big thanks to @twokul for pairing on this fix.

Fix #3586.
Clarify that you should not override Ember.View#destroyElement
Add ember-routing-loading-error-substates to FEATURES.

[ci skip]
Merge pull request #3621 from rjackson/add_loading_states_to_features

Add ember-routing-loading-error-substates to FEATURES.
Merge pull request #3610 from lukemelia/doc-tweak

Clarify that you should not override Ember.View#destroyElement
Merge pull request #3605 from rjackson/follow_rubygems_version_rules

Simplify rubygems version string.
Improves {{action}} helper docs

* Removed references to old-style view use
* Removed superfluous handlebars script tags
Merge pull request #3608 from hjdivad/fix-3586

[BUGFIX beta] reduceComputed handle out of range indexes.