Return int64 from buffer.Buffer.Delete.

You can delete int64 bytes, so we better be able to return that.
Rename buffer.Buffer to buffer.Bytes.

Eventually I will be adding buffer.Runes.
Change buffer.Address from a point address to a string address.
Unexport buffer.Bytes insert and delete.

This is a breaking change, because edit still uses these no-longer-exported methods.
Move a helper function to the bottom of the test file.

When I open the file, I want to see the tests, not details.
Add buffer.Bytes.Read and buffer.Bytes.Write.
Convert edit.Buffer to buffer.Runes.

This also removes the, now empty, edit package.
It'll be back, but focused on editing, not buffering.
Change Runes.Get and Runes.Put with Runes.ReadFrom and Runes.WriteTo.

Now it implements io.ReaderFrom and io.WriterTo.
Rename Read and Write to Get and Put to distinguish from io.Reader and io.Writer.
Add the elusive buffer/address.go.
Merge pull request #22 from eaburns/buffers

Convert edit.Buffer into buffer.Runes.