feat: non virtual interface idiom (nvi)

feat(type-traits): sfinae is_valid.

feat(sfinae): sfinae c++ idiom realization.

Merge branch 'develop'

Merge

fix: merging for WeakCallbackSubject

feat(sfinae): sfinae c++ idiom realization.

Merge branch 'develop'

fix: final alpha version of WeakCallbackSubject.

fix: unstable hash of WeakMethodInvoker.

fix: for WeakCallbackSubject work

fix: final alpha version of WeakCallbackSubject.

Merge

fix: merging for WeakCallbackSubject

fix: problems, when unit test WeakCallbackSubject

feat: WeakCallbackSubject, ObserverWeakMsg

feat: middle state. ObserverWeakMsg, WeakCallbackSubject

fix: problems, when unit test WeakCallbackSubject

feat: WeakCallbackSubject, ObserverWeakMsg

feat: middle state. ObserverWeakMsg, WeakCallbackSubject

fix: correction for observer pattern -WeakCallbackSubject

fix: merging

Merge branch 'develop' of gitlab.com-cpp-utility:FokinDenis88/cpp-utility into develop

fix: work on weak-callback-subject

doc: change header ----- to _____

doc: to-do tasks

feat: weak-ptr process with autoclean.

feat: new repo name

feat: autoclean in weak_ptr

feat: weak-ptr process with autoclean.

feat: new repo name

feat: autoclean in weak_ptr