cpp11 0.2.4

The preserve list is now more robust to invalid values, such as when the XPtr has no address or if non-xptr’s are stored in the option. This fixes errors when reloading packages using cpp11 and RStudio’s session restores.
The preserve list is now more robust to invalid values, such as null pointers when the XPtr is serialized. This situation occurs during ‘Install and Restart’ in RStudio (#121)

cpp11 0.2.3

r_vector::const_iterator::operator* is now a const method (#113, @bkietz, @xhochy)
The preserve list is now stored in an XPtr, rather than an environment, to avoid issues when serializing the preserve environment, which happens implicitly when RStudio or RStudio Cloud saves all options when resuming a session (#116)

r_bool added as an adapter between bool and Rboolean values (#57, @bkietz)
data_frame() objects now have the number of rows correctly set as real length, not the reserved length (#91)
Fixed potential memory leak in cpp11::writable classes.

cpp11 is now able to compile on gcc 4.8.5 (#69, @bkietz)
cpp_source(), cpp_function() and cpp_eval() now support [[cpp11::linking_to()]] syntax to link to third party packages with C++ headers. (#48)

as_cpp<E>() now works with enumeration types (#52, @bkietz)
as_cpp<int>() and as_cpp<double>() now implicitly coerce between all 3 types of single NA values (#53).
list::const_iterator::operator*() added so iterators could be used on list objects (#60, @romainfrancois)
safe[] can now work with functions that return any type (#70, @bkietz)
The END_CPP macro now includes a catch(...) block to catch all C++ exceptions that do not inherit from std::exception (#47).
Improve consistency of inserting NA values in r_string objects (#45)
Added a NEWS.md file to track changes to the package.