roxygenise dotprops
boundingbox returns matrix with class boundingbox

* this breaks an equality test or two but should have no major impact
update tests to reflect boundingbox class
doc: fix rdname for boundingbox.character

* so that it is documented and exported
minor doc fixes
boundingbox.list method (for shape3d type objects)
roxygenise @family directives
add test for boundingbox.list
teach boundingbox.default to handle data.frames

* also ensure that colnames are not passed on since this is consistent with
  past behaviour although not explicitly documented anywhere
examples of plot3d.boundingbox (and cross-refs)
dev: rstudio project settings for devtools

* check with devtools
* and roxygenise on check
Merge branch 'feature/boundingbox-shape3d'

* closes #137
* feature/boundingbox-shape3d:
  examples of plot3d.boundingbox (and cross-refs)
  teach boundingbox.default to handle data.frames
  add test for boundingbox.list
  roxygenise @family directives
  boundingbox.list method (for shape3d type objects)
  minor doc fixes
  doc: fix rdname for boundingbox.character
  update tests to reflect boundingbox class
  boundingbox returns matrix with class boundingbox
  roxygenise dotprops