Fix PROTECT error.
Remove UTF-8 characters from comments
ref() now handles custom classes properly (@yutannihilation, #36)
sxp() is a new tool for displaying the underlying C representation of an object (#38).
obj_size() now special cases the ALTREP “deferred string vectors” which previously crashed due to the way in which they abuse the pairlist type (#35).
ast() prints scalar integer and complex more accurately (#24)
obj_addr() no longer increments the reference count of its input (#25)
obj_size() now correctly computes size of ALTREP objects on R 3.5.0 (#32)