Added SlurmTree

[Gruek]

• Changed lua/Tree.lua to automatically distribute nodeIndexes if they are not specified.

• Changed lua/Tree.lua to take an optional argument for the function that builds the tree connections (defaults to "rcsvAllPairs")

• Added lua/SlurmTree.lua a tree implementation based on using slurm workload manager. (can also provide example of how to make use of SlurmTree with slurm jobs)

[nicholas-leonard]

@Gruek Can you update the Tree docs?

[Gruek]

@nicholas-leonard Do you just mean the README docs? Should I write a new paragraph specific to SlurmTree?

[mirandaconrado]

@Gruek Yes. It doesn't have to be long, but just to clarify why there's a new thing and when it should be used or not.

[Gruek]

@mirandaconrado @nicholas-leonard Done! :)

[nicholas-leonard]

@Gruek Thanks!

[mirandaconrado]

@Gruek docs and example? It must be my birthday. Thanks for the changes!