Remove bops, use Buffer instead

In PouchDB, we're attempting to get the MemDOWN plugin working in the browser as an alternative backend via leveldown (https://github.com/pouchdb/pouchdb/pull/2063, https://github.com/pouchdb/pouchdb/issues/1767).  Apparently bops is a no-go for the browser, so this replaces bops with Buffer.

Our own browser tests are passing, and in this project when I do npm test, it's all clear.  The one thing I'm unsure about is the `decode` line; it makes no sense to me why we'd want to return a string in the browser but a Buffer in Node.

So basically some guidance here would be much appreciated, but I think this PR is a good start, anyway.