Added basic authProvider code

Added bindings for authProvider (#12)

* added bindings for authProvider

* relaxed type constraint for authProvider to just a string to allow interop

* changed params of authProvider to more generic Js.Json.t type

* bumped version

* removed bs code that doesnt work since bs.as tag requires string literal and cant handle a variable

Readme update

Updated npm installation instructions in readme.

First Release

Shotgun approach of adding as much of the basic functionality as possible. The goal of this release is just to get react-admin working for ReasonML projects. For now, many of the binding types are much more permissive than they need to be. I am going to try to make the binding types much stricter in future releases.