v42.1.0: Version 42.1.0 of ppx_deriving packaged for BuckleScript.

Of note, the corresponding version of `ppx-deriving` is *not* included, due to a recursively mutual dependency. These packages are, however, properly packaged on npm:

    npm install --save bs-deriving@42.1.0
    npm install --save-dev ppx-deriving@42.1.0

If you wish to acquire them via git, ensure you manually pull the matching version of my `ppx-deriving` package! The submodule linkage recorded in the repository will be perpetually one release behind.