This will make setting the playtime for the engine easier since
the current savestate stores it as a string.
This value gets set at the same time that the string playtime gets set.
Custom deleters of ScopedPtr are not currently fully conforming to
C++11's support for custom deleters in std::unique_ptr for the
sake of simplicity of implementation. Unlike in the standard
library, plain functions and lvalue references are not supported,
nor may custom deleters be passed to the constructor at runtime.
This can be improved in the future, if necessary, by doing what
standard library implementations usually do and creating a Pair
class that uses the Empty Base Optimization idiom to avoid extra
storage overhead of the deleter instance when it is not needed, as
in typical standard library implementations, plus some additional
type traits to support the necessary metaprogramming for the
different type overloads.
Now SaveStateDescriptor no longer subclasses HashMap. Instead all possible
saved meta data is included directly into SaveStateDescriptor.
This is slightly less flexible, but we never needed that flexibility so far.
On the other hand it should reduce the memory usage. At least on my system
(Linux/amd64) the old SaveStateDescriptor had a size of 928 and the new
SaveStateDescriptor has a size of 200.
