Add more operations

[BrettWitty]

This is a nice, mutable Interval Tree implementation. I was hoping for more operations (especially mutating ones), as in this Python library: https://github.com/chaimleib/intervaltree

In particular, I was interested in chop (trim/remove nodes intersecting with an interval), which I think requires a bunch of other functionality.

[zaeleus]

Hi @BrettWitty!

I have no immediate plans to implement mutable operations other than insertion, but I'll consider it for the future. The application in which I wrote this library strictly uses it for lookups after build.