ensure that nlapply (and therefore xform etc) produce identical output with neuronlistfh

* just a matter of looking after classes
test equivalence of neuronlist(fh) arithmetic
Merge branch 'feature/neuronlistfh'

* feature/neuronlistfh:
  test equivalence of neuronlist(fh) arithmetic
  ensure that nlapply (and therefore xform etc) produce identical output with neuronlistfh
fix visibility of as.neuron.default (required for reading neurons)
don't call as.neuronlistfh.filehash method explicitly

* as this messes up downstream method dispatch
move logic of as.neuronlistfh.filehash to as.neuronlistfh.default

* thereby implementing stashR support
Docs for neuronlistfh including e.g. of new stashR functionality
Just test if the db object extends filehash - anyone should do
Fixes for neuronlistfh docs
fix example of reloading neuronlistfh

neuronlist() function doesn't exist at the moment
filehash test when no df available

* thought this was necessary, but turns out NULL[1,] is just NULL
  not an error
import methods::is

* I think is necessary because although methods is always available it may not
  always be attached
make stashR a valid backend for as.neuronlistfh.neuronlist
fix [.neuronlistfh when backed by stashR remoteDB

This didn't work because there is no [ method for stashR dbs
test creation, saving and conversion of stashR backed neuronlists
roxygenise
fix specification of path in test-neuronlistfh

* was leaving crud behind
make sure that additional arguments are passed to new() when making stashR backend

* otherwise e.g. url would not get passed to remoteDB
Add stashR as suggested package

* just suggested because it's obviously not essential
* should maybe think about doing the same with filehash
Merge branch 'feature/stashr'

* feature/stashr:
  Add stashR as suggested package
  make sure that additional arguments are passed to new() when making stashR backend
  fix specification of path in test-neuronlistfh
  roxygenise
  test creation, saving and conversion of stashR backed neuronlists
  fix [.neuronlistfh when backed by stashR remoteDB
  make stashR a valid backend for as.neuronlistfh.neuronlist
  import methods::is
  filehash test when no df available
  fix example of reloading neuronlistfh
  Fixes for neuronlistfh docs
  Just test if the db object extends filehash - anyone should do
  Docs for neuronlistfh including e.g. of new stashR functionality
  move logic of as.neuronlistfh.filehash to as.neuronlistfh.default
  don't call as.neuronlistfh.filehash method explicitly