Start using Rstudio

* now that it has debugging capabilities
Much faster processing of dates
speed up reading of user variables/strings

* really no reason to use eval/parse here AFAICS
  I think I must have been thinking this way because
  it is require for assigning nested list elements
no need to keep source in parse calls

* can't get read of these parse calls, but there's
  certainly no reason to keep source (which seems
  to take about 2/3 of the call time for parse).
Switch depends to imports

* as per latest recommendations
Change regex form to remove a check() warning

* I think the problem is how roxygen handles escaping
  of arguments but can easily get round it so ...
fix bug in parsing of dates

* revealed by build_win in different time zone
Prepare v0.6