0.29.0 - Updated Interaction API & Housekeeping

Updated Interaction API & Housekeeping
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API Breaks
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- The `Interaction` API has changed. Rather than calling `Interaction(component..).registerWithComponent`, now you create the interaction first `var interaction = new Interaction(...)` and then attach it to a `Component` using `Component.registerInteraction(interaction)`.
- Additionally, `Interaction.Click`s now have a consistent callback api that uses `Point`s.

API Extensions:
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- `Plot.attr` now exists as an alias to `Plot.project`, and is the preferred invocation as it matches D3 semantices for the function of the same name.

Bugfixes:
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- `PercentageFormatter` behavior is improved.
- Autodomaining no longer fails if the data is of an incorrect-but-coercible type.

Housekeeping:
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- `Component.renderTo(selection)` now gives helpful error messages if something goes wrong.
- `README` updated
- Bower/NPM flavor text improved