* Code clean-up and safety (#46)

* code safety

* remove dependence on qrng

* some cleanup

* avoid lower > upper by reversing the grid at the right places

* ensure non-NaN bandwidth

* unused variable

* add randtoolbox to Imports

* Prepare patch (#47)

* code safety

* remove dependence on qrng

* some cleanup

* avoid lower > upper by reversing the grid at the right places

* ensure non-NaN bandwidth

* unused variable

* add randtoolbox to Imports

* update NEWS and DESCRIPTION

* update API docs

* update CRAN comments