Give nlapply an OmitFailures argument
test nlapply with OmitFailures

* all 3 variants
Don’t print error messages when OmitFailures=T/F
Give nmapply an OmitFailures argument as well
dev: add more contexts for neuronlist tests
roxygenise
Merge branch 'feature/nlapply-failures'

* closes #141
* feature/nlapply-failures:
  roxygenise
  dev: add more contexts for neuronlist tests
  Give nmapply an OmitFailures argument as well
  Don’t print error messages when OmitFailures=T/F
  test nlapply with OmitFailures
  Give nlapply an OmitFailures argument
Give nlapply a subset argument

* and use it in xform and mirror.neuronlist
* also includes a test
doc: mirror(.neuronlist) doc fixes
Give mirror.neuronlist OmitFailures arg

* this and subset will be passed on to nlapply
docs: small fixes to dotprops docs
add example listing all neuronlist methods
missing docs for as.neuronlist.default
more neuronlist doc fixes/additions
give dotprops.neuronlist OmitFailures argument

* will be handled by nlapply
Merge branch 'feature/nlapply-failures'

* feature/nlapply-failures:
  give dotprops.neuronlist OmitFailures argument
  more neuronlist doc fixes/additions
  missing docs for as.neuronlist.default
  add example listing all neuronlist methods
  docs: small fixes to dotprops docs
  Give mirror.neuronlist OmitFailures arg
  doc: mirror(.neuronlist) doc fixes
  Give nlapply a subset argument
fix subset.neuronlist handling of numeric indices

* fixes #142
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