Delete (and Insert?) code is O(n^2)

[driusan]

There's various places in the editing code that do things like
newBuffer := make([]byte, size)
copy(newBuffer, oldBuffer)
copy(newBuffer[start:], stuff)
copy(newBuffer[end:], oldBuffer[offset:])

to insert or delete from the middle of a buffer. It's been pointed out that this is quadratic.

This isn't an issue or even noticeable for average-sized source code files, but is going to be an issue for editing very text files.