v0.6.0

Breaking

1. The ref directive does something different now (see below)
2. The ref property on components is now called refs and holds Refs not elements (see below)

Fixes

1. Previous value now linked to point of use, not read, which was causing inconsistent updates after visibility toggles.
2. Can now use attributes which are not valid property names, e.g. xxx-yyy.
3. Fix issue with validating Xargs access in expressions.

Features

1. The ref:xyz directive now creates a Ref object accessible as this.refs.xyz which has:
   1. Property node which points to the corresponding element or component as applicable.
   2. Method update which updates the tree below that, allowing very easy partial updates.
2. Xargs now includes props.

Other

1. Further performance improvements (now faster than riot).
2. Further bundle size reductions.
3. Added logo and usage section to README.
4. Updated performance screenshots.