tweak spine tests

* testing at full precision is probably asking for trouble on some platform
* may as well verify that we get a neuron back
add weights option to ngraph

* closes #85
test that weights can be calculated and set
simplify spine function using new weights option of ngraph
simplify spine by removing PlotPath option and internal spinify function

* would rather just return a neuron and let user plot it herself if required
* change default behaviour to return the neuron rather than distance
Add as.im3d generic (with no actual methods)
Add test for setting weights explicitly in as.ngraph
Add missing documentation for ... argument
Merge branch 'im3d' of github.com:ajdm/nat into ajdm-im3d

* 'im3d' of github.com:ajdm/nat:
  Add missing documentation for ... argument
  Add as.im3d generic (with no actual methods)
add a pass-through as.im3d.im3d method

* with docs
updating @family directives
Merge branch 'ajdm-im3d'

* ajdm-im3d:
  updating @family directives
  add a pass-through as.im3d.im3d method
  Add missing documentation for ... argument
  Add as.im3d generic (with no actual methods)
Bump version to 1.4.9