FeatStd Memory Management

Removed Sharing Object

The outdated and orphaned file SharingObject.h has been removed.

Retain Count atomic and uncopyable

The retain count of shared objects - enabled by macro "FEATSTD_SHARED_POINTER_DECLARATION" - has been made atomic to make increments and decrements thread-safe. Additionally the retain count has been made uncopyable to avoid copying the retain count when cloning shared objects.