Added Preact support

[XavierLeTohic]

Ref #134

You can find a working preact app exemple with rc-form here

Please note that I bypassed pre-commit linter because the installed "preact" and "preact-compat" packages are not used in the code but required to make rc-form works with preact.

[benjycui]

No package-lock.json, thanks.

And I think you should add test to make sure rc-form works with preact.

[XavierLeTohic]

With enzyme we need to make aliases of react testing packages to preact testing packages.
But in this case the existing tests will be launch with preact aliases instead of react.

The solution is to write a configuration file only for testing with preact and run another task named "test:preact" that will use this configuration.

Do you know any alternative way to do it ? 🤔

Thanks