Various changes and comments

You might want to review the commits one by one to read the comments.

I haven't tested any of this.

As I said via email, I would expect the Go version to be at least twice as fast as Python (but maybe that is unreasonable).  I didn't see any obvious performance issues here.  But I didn't run a profiler on it either.  Perhaps the `LimitReader` isn't as performant as it could be (for example).

But here are some comments for now.  Be sure to test them.  In fact, you might even want to create a `mocleaner_test.go` file to create some tests for these functions.  I'd propose creating a directory full of sample text that you can test against.  I started testing with `testify` (pretty simple to get started with).  I've now graduated to `ginkgo` which has a lot more functionality but also a little more difficult to get started with.