Add inertia() helper function

[georgehanson]

@reinink This is a re-open on my previous PR #29.

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When using the Laravel framework I personally find it cleaner to use the view(), so I'd also really like to be able to use the same approach with Intertia.

This pull request simply adds a helper function inertia().

For example:

return Intertia::render('Welcome', ['name' => 'George']);

becomes

return inertia('Welcome', ['name' => 'George']);

You can also access the ResponseFactory instance by not passing any parameters to the function. This allows you to make calls to other methods such as share.

inertia()->share('name', 'George');

[reinink]

Dig it, thanks @georgehanson.