abstraction of nodes, indexing no longer needs to be linear, but could be any label
error if spm not found on path
data loading for subject and creation of tree structure
return self in functions such as set_value
minor changes, cleaning branch
parallelisation efforts
added correlation matrices
nice example
nice example of ill-conditioning
moved hierarchical tree construction to the htree file
changed tree creation process to 'HTree(list).create()'
re-parallelisation and crossvalidation over h
made creation of tree compatible with new create() api