Add custom attribute mapping feature

[yume-chan]

I'm using this package with React Router. React Router has a <NavLink> component which has an activeClassName attribute, to be appended to its className when it's active.

However, I think it's extreme ugly when I can use styleName everywhere except here.

At first I want to extend the support to any attribute names ending with styleName/StyleName, but at last I added this attributeNames option to allow customization of the transformation. Each key represents a source attribute name and the corresponding value represents the destination attribute name. I think this feature can make it more easily to deal with components with multiple states, or with multiple xxxClassName attributes.

The default value is { "styleName": "className" } to keep backward compatibility, and the specified object will be merged with this default value unless it contains a different value for styleName.

A very rare (maybe just non-exist) use case will be setting styleName to something else or null. It just means the transformation process is totally controllable.

[gajus]

Thank you

[ebramanti]

@gajus Can you run a release for this? Currently having to use my own branch for this feature.

[jus-jus]

This feature is missing in my react-router setup. It would be great to have it without checking out @yume-chan branch.
Is it expected to have this one released soon?