Tree (octree)

Hi Chris,

great project, my best compliments!

I would like to contribute if you like. In the past I have developed a generic container (based on an unlimited polymorphic class) with an octree structure (it was an hash table with single linked list for resolving keys conflicts on the single slot). I would like to contribute to your FIAT working on trees, how can I do?

Do you have some contributing guidelines?
Do you have some references for the trees you want to implement?
Do you have a _preferred collaborative model_ (e.g. fork/pull-request)?

In my modest opinion, one of the worst lack of Fortran is the absence of generic containers, your FIAT is very appreciated.

My best regards.