v20.0.0: Version 20.0.0 of Sedlexing, packaged for BuckleScript.

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

    npm install --save bs-sedlex@20.0.0
    npm install --save-dev ppx-sedlex@20.0.0

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