envir 0.3.0

• attach_source() now allows the R scripts to contain library() calls, and have
  functions defined in the script "see" the library() calls. R scripts are now
  first sourced into a new.env(parent = .GlobalEnv), and then all symbols are
  subsequently copied over into a (different) attached environment. You can restore
  the old behavior, where the scripts are evaluated in an already attached environment,
  with attach_source(parent = NULL).

• attach_source() now allows scripts to define a .mask.OK object to a character
  vector of names of objects that shouldn't be warned about when warn.conflicts=TRUE.

• attach_source() now respects the existence of .conflicts.OK, matching the
  behavior of attach().

• attach_source() gains a parent argument, allow customizing the parent of
  the environment where scripts will be evaluated. (default, .GlobalEnv)