v0.3.0 of touch_targets

Create overflowing touch targets to make accessible design-sized components.

Changelog excerpt:

• Performed element renames:

  • TouchClient.childSize→ TouchClient.innerSize;
• TouchClient.hitTestFrom()→ TouchClient.hitTestInnerFrom();

• TouchTargetBehavior→ TouchTargetFit(behavior→ fit).

• Refactored RenderTouchTargetMixininto three mixins: base TouchClientRenderObjectBaseMixin, optional TouchClientRenderObjectOptionalMixinand required TouchClientRenderObjectRequiredMixin.

• Added documentation comments to some elements.

• Minor internal changes.