V1.0

Wrote a mutable tree class that I may use later with Needs in economics.
I'm merging it into the master branch, though, in the hope that it will
be useful to others.
Merge pull request #6 from CS-196-Space-Colonization/tree

V1.0 - Wrote a mutable tree class that I may use later with Needs in economics.
I'm merging it into the master branch, though, in the hope that it will
be useful to others.