Also some changes to make sandbox things work with the new casting
Made it so base_class doesn't need to know about polymorphism to work
All relates to #188
count_in/out_serializers will now count the number of specializations if a type is
specialized, otherwise it will count the number of non-specialized serialization functions.
as a result of this, is_output/input_serializable now works as you would expect from the name
and will return true for correctly configured specialized types too.
this caused some logic changes to need to happen in cereal.hpp, mostly within the PROCESS_IF macro.
added some tests related to this change and #180fixes#180
In sandbox_vs.cpp, there is a very strange issue with calling
traits::is_input_serializable that causes icc 15.0.0 to crash.
Everything else works great though.
Added a set of trait classes that can be used to get an input archive
from an output archive. Requires specializing a struct for each direction or
alternatively using the new macro CEREAL_SETUP_ARCHIVE_TRAITS(InArchive, OutArchive).
This has already been added for all built in archive types. This is currently only
used for minimal serialization.
load_minimal type traits now correctly use the output archive to check the existence of
a corresponding save_minimal and get its return type, using the new get_input_from_output
type class.
Added a test for this case into the minimal structs test.
Sandbox_vs needed the new macro to become compliant.
