add inline doc for deprecated Ember.State/StateManager

to close #3316
Merge pull request #3321 from bradoyler/patch-1

add inline doc for deprecated Ember.State/StateManager
Add defeatureify to Travis config.
Incorrect error message in router.js
Merge pull request #3325 from rutinerad/patch-1

Incorrect error message in router.js
Improve message and logic around UnrecognizedURLError
Merge pull request #3326 from trek/improve-message-and-logic-for-unrecognzied-urls

Improve message and logic around UnrecognizedURLError
Only throw an initialValue error if it is null or undefined (i.e. not 0 or some other falsy value)
Merge pull request #3327 from matthooks/master

Allow reduceComputed to have an initial value of 0.
Add shortcut for whitelisting all modifier keys on {{action}}
Modifier key-independent action helper use cases can be less verbose and more future-proof.
fixing grammer in computed property docs
Merge pull request #3335 from GavinJoyce/master

fixing grammer in computed property docs
Merge pull request #3323 from codefox421/action-modkeys-any

Add shortcut to action helper for whitelisting all modifier keys
Add test for using concatenated properties with functions
Close #3307 – Fix unexpected behavior with functions in concatenated properties
Fix grammar in CONTRIBUTING.md
Improve docs for CoreObject#concatenatedProperties
Documents `{{link-to "route" someId}}` behavior
Update link_to.js

add description for `disabled` and `disabledWhen` properties for `link-to` handlebar helper.
components should declare actions in the actions hash