Verbatim version of nat.as::InterpolateAlongNeuron
basic implementation of resample.neuron

* dependent functions
Always recalculate seglengths
Add test for resample.neuron
Add two more tests that reveal bugs in resample.neuron
Fix bug in resample.neuron
Consistent return values for as.seglist.neuron

* always returns list of lists when all=TRUE
  even when there is only one subtree
update resample docs inc FIXME resample.neuron

* resample.neuron doesn’t handle width or multiple subtrees
give seglengths a flatten option (true by default)

* i.e. can return list of seglengths vectors for each
  subtree
Merge branch 'feature/resample-neuron'

* feature/resample-neuron:
  update resample docs inc FIXME resample.neuron
  Fix bug in resample.neuron
  Add two more tests that reveal bugs in resample.neuron
  Add test for resample.neuron
  Always recalculate seglengths
  basic implementation of resample.neuron
  Verbatim version of nat.as::InterpolateAlongNeuron