Chart.layouts seems more consistent with other service names (Chart.plugins, Chart.scales, etc.) but also more inline with the service which handle many layout (one per charts).
For consistency, enable ESLint `one-var` rule to require multiple variable declarations for initialized variables per scope. Uninitialized variables can still be declared together (preferred) or separately.
http://eslint.org/docs/rules/one-var
Default options can now be accessed by importing `core/core.defaults`. The returned object acts as a singleton and is populated when importing classes that expose their own default values (meaning that importing only `code.defaults` results in an empty object). Also make `Chart.Ticks` and `Chart.Interaction` importable since existing defaults rely on these values.
Add the `defaults._set` method that make easier declaring new defaults by merging given values with existing ones for a specific scope (`global`, `scale`, `bar`, etc).
Properly export helpers and remove dependencies to `Chart.helpers`. Helpers can now be accessed from `src/helpers/index.js` (`var helpers = require('path/to/helpers/index')`, instead of `var helpers = Chart.helpers`).
The `clone` method now accepts any type of input but also recursively perform a deep copy of the array items. Rewrite the `configMerge` and `scaleMerge` helpers which now rely on a new generic and customizable `merge` method, that one accepts a target object in which multiple sources are deep copied. Note that the target (first argument) is not cloned and will be modified after calling `merge(target, sources)`. Add a `mergeIf` helper which merge the source properties only if they do not exist in the target object.
For consistency with `valueOrDefault`, `valueAtIndexOrDefault` now returns null if `value` (expected array) is null. Also get rid of the superfluous `get` prefix in `getValueOrDefault` and `getValueAtIndexOrDefault`.
Move some of the "core" and "canvas" utils in `helpers.core.js` and `helpers.canvas.js` and introduce the new `isNullOrUndef` and `isObject` helpers. Deprecate `indexOf` and rename `drawRoundedRectangle` to `roundedRect` which now creates a simple `rect` path if radius is 0. Write missing unit tests for the moved helpers.
