Rewrites unspecialized SmalltalkVM::newObject<T> with static_cast

Issue: #38
Adds static_cast into hptr_base

Issue: #38
Adds static_cast to specialized SmalltalkVM::newObject<>()

Issue: #38
Fixes casts in pointer arithmetic in memory managers

Issue: #38
Fixes specific casts in memory managers

Issue: #38
Replaces a lot of C-style casts with static_cast

Issue: #38